hw/9pfs/9p-synth.c | 18 +++++++++++++++--- hw/9pfs/9p-synth.h | 5 +++++ hw/9pfs/codir.c | 3 +-- include/qemu/osdep.h | 13 +++++++++++++ util/osdep.c | 21 +++++++++++++++++++++ 5 files changed, 55 insertions(+), 5 deletions(-)
`struct dirent' returned from readdir(3) could be shorter (or longer)
than `sizeof(struct dirent)', thus memcpy of sizeof length will overread
into unallocated page causing SIGSEGV. Example stack trace:
#0 0x00005555559ebeed v9fs_co_readdir_many (/usr/bin/qemu-system-x86_64 + 0x497eed)
#1 0x00005555559ec2e9 v9fs_readdir (/usr/bin/qemu-system-x86_64 + 0x4982e9)
#2 0x0000555555eb7983 coroutine_trampoline (/usr/bin/qemu-system-x86_64 + 0x963983)
#3 0x00007ffff73e0be0 n/a (n/a + 0x0)
While fixing this, provide a helper for any future `struct dirent' cloning.
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/841
Cc: qemu-stable@nongnu.org
Co-authored-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Reviewed-by: Dmitry V. Levin <ldv@altlinux.org>
Signed-off-by: Vitaly Chikunov <vt@altlinux.org>
---
Tested on x68-64 Linux with btrfs-progs tests and qos-test -m slow.
Changes since v4:
- Zero clear V9fsSynthOpenState on allocation. Uninitialised use of
d_reclen bug found by fuzzing. Use g_new0 instead of g_malloc0 as
Greg Kurz suggested.
hw/9pfs/9p-synth.c | 18 +++++++++++++++---
hw/9pfs/9p-synth.h | 5 +++++
hw/9pfs/codir.c | 3 +--
include/qemu/osdep.h | 13 +++++++++++++
util/osdep.c | 21 +++++++++++++++++++++
5 files changed, 55 insertions(+), 5 deletions(-)
diff --git a/hw/9pfs/9p-synth.c b/hw/9pfs/9p-synth.c
index b38088e066..396cda36f1 100644
--- a/hw/9pfs/9p-synth.c
+++ b/hw/9pfs/9p-synth.c
@@ -182,7 +182,12 @@ static int synth_opendir(FsContext *ctx,
V9fsSynthOpenState *synth_open;
V9fsSynthNode *node = *(V9fsSynthNode **)fs_path->data;
- synth_open = g_malloc(sizeof(*synth_open));
+ /*
+ * V9fsSynthOpenState contains 'struct dirent' which have OS-specific
+ * properties, thus it's zero cleared on allocation here and below
+ * in synth_open.
+ */
+ synth_open = g_new0(V9fsSynthOpenState, 1);
synth_open->node = node;
node->open_count++;
fs->private = synth_open;
@@ -220,7 +225,14 @@ static void synth_rewinddir(FsContext *ctx, V9fsFidOpenState *fs)
static void synth_direntry(V9fsSynthNode *node,
struct dirent *entry, off_t off)
{
- strcpy(entry->d_name, node->name);
+ size_t sz = strlen(node->name) + 1;
+ /*
+ * 'entry' is always inside of V9fsSynthOpenState which have NAME_MAX
+ * back padding. Ensure we do not orerflow it.
+ */
+ g_assert(sizeof(struct dirent) + NAME_MAX >=
+ offsetof(struct dirent, d_name) + sz);
+ memcpy(entry->d_name, node->name, sz);
entry->d_ino = node->attr->inode;
entry->d_off = off + 1;
}
@@ -266,7 +278,7 @@ static int synth_open(FsContext *ctx, V9fsPath *fs_path,
V9fsSynthOpenState *synth_open;
V9fsSynthNode *node = *(V9fsSynthNode **)fs_path->data;
- synth_open = g_malloc(sizeof(*synth_open));
+ synth_open = g_new0(V9fsSynthOpenState, 1);
synth_open->node = node;
node->open_count++;
fs->private = synth_open;
diff --git a/hw/9pfs/9p-synth.h b/hw/9pfs/9p-synth.h
index 036d7e4a5b..eeb246f377 100644
--- a/hw/9pfs/9p-synth.h
+++ b/hw/9pfs/9p-synth.h
@@ -41,6 +41,11 @@ typedef struct V9fsSynthOpenState {
off_t offset;
V9fsSynthNode *node;
struct dirent dent;
+ /*
+ * Ensure there is enough space for 'dent' above, some systems have a
+ * d_name size of just 1, which would cause a buffer overrun.
+ */
+ char dent_trailing_space[NAME_MAX];
} V9fsSynthOpenState;
int qemu_v9fs_synth_mkdir(V9fsSynthNode *parent, int mode,
diff --git a/hw/9pfs/codir.c b/hw/9pfs/codir.c
index 032cce04c4..c0873bde16 100644
--- a/hw/9pfs/codir.c
+++ b/hw/9pfs/codir.c
@@ -143,8 +143,7 @@ static int do_readdir_many(V9fsPDU *pdu, V9fsFidState *fidp,
} else {
e = e->next = g_malloc0(sizeof(V9fsDirEnt));
}
- e->dent = g_malloc0(sizeof(struct dirent));
- memcpy(e->dent, dent, sizeof(struct dirent));
+ e->dent = qemu_dirent_dup(dent);
/* perform a full stat() for directory entry if requested by caller */
if (dostat) {
diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index d1660d67fa..ce12f64853 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -805,6 +805,19 @@ static inline int platform_does_not_support_system(const char *command)
}
#endif /* !HAVE_SYSTEM_FUNCTION */
+/**
+ * Duplicate directory entry @dent.
+ *
+ * It is highly recommended to use this function instead of open coding
+ * duplication of @c dirent objects, because the actual @c struct @c dirent
+ * size may be bigger or shorter than @c sizeof(struct dirent) and correct
+ * handling is platform specific (see gitlab issue #841).
+ *
+ * @dent - original directory entry to be duplicated
+ * @returns duplicated directory entry which should be freed with g_free()
+ */
+struct dirent *qemu_dirent_dup(struct dirent *dent);
+
#ifdef __cplusplus
}
#endif
diff --git a/util/osdep.c b/util/osdep.c
index 42a0a4986a..67fbf22778 100644
--- a/util/osdep.c
+++ b/util/osdep.c
@@ -33,6 +33,7 @@
extern int madvise(char *, size_t, int);
#endif
+#include <dirent.h>
#include "qemu-common.h"
#include "qemu/cutils.h"
#include "qemu/sockets.h"
@@ -615,3 +616,23 @@ writev(int fd, const struct iovec *iov, int iov_cnt)
return readv_writev(fd, iov, iov_cnt, true);
}
#endif
+
+struct dirent *
+qemu_dirent_dup(struct dirent *dent)
+{
+ size_t sz = 0;
+#if defined _DIRENT_HAVE_D_RECLEN
+ /* Avoid use of strlen() if platform supports d_reclen. */
+ sz = dent->d_reclen;
+#endif
+ /*
+ * Test sz for zero even if d_reclen is available
+ * because some drivers may set d_reclen to zero.
+ */
+ if (sz == 0) {
+ /* Fallback to the most portable way. */
+ sz = offsetof(struct dirent, d_name) +
+ strlen(dent->d_name) + 1;
+ }
+ return g_memdup(dent, sz);
+}
--
2.33.0
On Mittwoch, 16. Februar 2022 19:18:21 CET Vitaly Chikunov wrote: > `struct dirent' returned from readdir(3) could be shorter (or longer) > than `sizeof(struct dirent)', thus memcpy of sizeof length will overread > into unallocated page causing SIGSEGV. Example stack trace: > > #0 0x00005555559ebeed v9fs_co_readdir_many (/usr/bin/qemu-system-x86_64 + > 0x497eed) #1 0x00005555559ec2e9 v9fs_readdir (/usr/bin/qemu-system-x86_64 > + 0x4982e9) #2 0x0000555555eb7983 coroutine_trampoline > (/usr/bin/qemu-system-x86_64 + 0x963983) #3 0x00007ffff73e0be0 n/a (n/a + > 0x0) > > While fixing this, provide a helper for any future `struct dirent' cloning. > > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/841 > Cc: qemu-stable@nongnu.org > Co-authored-by: Christian Schoenebeck <qemu_oss@crudebyte.com> > Reviewed-by: Dmitry V. Levin <ldv@altlinux.org> > Signed-off-by: Vitaly Chikunov <vt@altlinux.org> > --- > Tested on x68-64 Linux with btrfs-progs tests and qos-test -m slow. Consider donating your Tested-by tag then. > Changes since v4: > - Zero clear V9fsSynthOpenState on allocation. Uninitialised use of > d_reclen bug found by fuzzing. Use g_new0 instead of g_malloc0 as > Greg Kurz suggested. I can confirm that v4 triggered the previously discussed ASan error when running the 9p 'synth' tests; and with this v5 ASan no longer triggers an error. Tested-by: Christian Schoenebeck <qemu_oss@crudebyte.com> Maybe some of the new comments could be improved, for instance ... > > hw/9pfs/9p-synth.c | 18 +++++++++++++++--- > hw/9pfs/9p-synth.h | 5 +++++ > hw/9pfs/codir.c | 3 +-- > include/qemu/osdep.h | 13 +++++++++++++ > util/osdep.c | 21 +++++++++++++++++++++ > 5 files changed, 55 insertions(+), 5 deletions(-) > > diff --git a/hw/9pfs/9p-synth.c b/hw/9pfs/9p-synth.c > index b38088e066..396cda36f1 100644 > --- a/hw/9pfs/9p-synth.c > +++ b/hw/9pfs/9p-synth.c > @@ -182,7 +182,12 @@ static int synth_opendir(FsContext *ctx, > V9fsSynthOpenState *synth_open; > V9fsSynthNode *node = *(V9fsSynthNode **)fs_path->data; > > - synth_open = g_malloc(sizeof(*synth_open)); > + /* > + * V9fsSynthOpenState contains 'struct dirent' which have OS-specific > + * properties, thus it's zero cleared on allocation here and below > + * in synth_open. > + */ > + synth_open = g_new0(V9fsSynthOpenState, 1); > synth_open->node = node; > node->open_count++; > fs->private = synth_open; > @@ -220,7 +225,14 @@ static void synth_rewinddir(FsContext *ctx, > V9fsFidOpenState *fs) static void synth_direntry(V9fsSynthNode *node, > struct dirent *entry, off_t off) > { > - strcpy(entry->d_name, node->name); > + size_t sz = strlen(node->name) + 1; > + /* > + * 'entry' is always inside of V9fsSynthOpenState which have NAME_MAX > + * back padding. Ensure we do not orerflow it. > + */ ... here is a typo in the comment. But unless there are more issues, I could handle such minor comment issues on my end before pushing. Reviewed-by: Christian Schoenebeck <qemu_oss@crudebyte.com> Best regards, Christian Schoenebeck > + g_assert(sizeof(struct dirent) + NAME_MAX >= > + offsetof(struct dirent, d_name) + sz); > + memcpy(entry->d_name, node->name, sz); > entry->d_ino = node->attr->inode; > entry->d_off = off + 1; > } > @@ -266,7 +278,7 @@ static int synth_open(FsContext *ctx, V9fsPath *fs_path, > V9fsSynthOpenState *synth_open; > V9fsSynthNode *node = *(V9fsSynthNode **)fs_path->data; > > - synth_open = g_malloc(sizeof(*synth_open)); > + synth_open = g_new0(V9fsSynthOpenState, 1); > synth_open->node = node; > node->open_count++; > fs->private = synth_open; > diff --git a/hw/9pfs/9p-synth.h b/hw/9pfs/9p-synth.h > index 036d7e4a5b..eeb246f377 100644 > --- a/hw/9pfs/9p-synth.h > +++ b/hw/9pfs/9p-synth.h > @@ -41,6 +41,11 @@ typedef struct V9fsSynthOpenState { > off_t offset; > V9fsSynthNode *node; > struct dirent dent; > + /* > + * Ensure there is enough space for 'dent' above, some systems have a > + * d_name size of just 1, which would cause a buffer overrun. > + */ > + char dent_trailing_space[NAME_MAX]; > } V9fsSynthOpenState; > > int qemu_v9fs_synth_mkdir(V9fsSynthNode *parent, int mode, > diff --git a/hw/9pfs/codir.c b/hw/9pfs/codir.c > index 032cce04c4..c0873bde16 100644 > --- a/hw/9pfs/codir.c > +++ b/hw/9pfs/codir.c > @@ -143,8 +143,7 @@ static int do_readdir_many(V9fsPDU *pdu, V9fsFidState > *fidp, } else { > e = e->next = g_malloc0(sizeof(V9fsDirEnt)); > } > - e->dent = g_malloc0(sizeof(struct dirent)); > - memcpy(e->dent, dent, sizeof(struct dirent)); > + e->dent = qemu_dirent_dup(dent); > > /* perform a full stat() for directory entry if requested by caller > */ if (dostat) { > diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h > index d1660d67fa..ce12f64853 100644 > --- a/include/qemu/osdep.h > +++ b/include/qemu/osdep.h > @@ -805,6 +805,19 @@ static inline int > platform_does_not_support_system(const char *command) } > #endif /* !HAVE_SYSTEM_FUNCTION */ > > +/** > + * Duplicate directory entry @dent. > + * > + * It is highly recommended to use this function instead of open coding > + * duplication of @c dirent objects, because the actual @c struct @c dirent > + * size may be bigger or shorter than @c sizeof(struct dirent) and correct > + * handling is platform specific (see gitlab issue #841). > + * > + * @dent - original directory entry to be duplicated > + * @returns duplicated directory entry which should be freed with g_free() > + */ > +struct dirent *qemu_dirent_dup(struct dirent *dent); > + > #ifdef __cplusplus > } > #endif > diff --git a/util/osdep.c b/util/osdep.c > index 42a0a4986a..67fbf22778 100644 > --- a/util/osdep.c > +++ b/util/osdep.c > @@ -33,6 +33,7 @@ > extern int madvise(char *, size_t, int); > #endif > > +#include <dirent.h> > #include "qemu-common.h" > #include "qemu/cutils.h" > #include "qemu/sockets.h" > @@ -615,3 +616,23 @@ writev(int fd, const struct iovec *iov, int iov_cnt) > return readv_writev(fd, iov, iov_cnt, true); > } > #endif > + > +struct dirent * > +qemu_dirent_dup(struct dirent *dent) > +{ > + size_t sz = 0; > +#if defined _DIRENT_HAVE_D_RECLEN > + /* Avoid use of strlen() if platform supports d_reclen. */ > + sz = dent->d_reclen; > +#endif > + /* > + * Test sz for zero even if d_reclen is available > + * because some drivers may set d_reclen to zero. > + */ > + if (sz == 0) { > + /* Fallback to the most portable way. */ > + sz = offsetof(struct dirent, d_name) + > + strlen(dent->d_name) + 1; > + } > + return g_memdup(dent, sz); > +}
On Thu, Feb 17, 2022 at 10:26:37AM +0100, Christian Schoenebeck wrote: > On Mittwoch, 16. Februar 2022 19:18:21 CET Vitaly Chikunov wrote: > > `struct dirent' returned from readdir(3) could be shorter (or longer) > > than `sizeof(struct dirent)', thus memcpy of sizeof length will overread > > into unallocated page causing SIGSEGV. Example stack trace: > > > > #0 0x00005555559ebeed v9fs_co_readdir_many (/usr/bin/qemu-system-x86_64 + > > 0x497eed) #1 0x00005555559ec2e9 v9fs_readdir (/usr/bin/qemu-system-x86_64 > > + 0x4982e9) #2 0x0000555555eb7983 coroutine_trampoline > > (/usr/bin/qemu-system-x86_64 + 0x963983) #3 0x00007ffff73e0be0 n/a (n/a + > > 0x0) > > > > While fixing this, provide a helper for any future `struct dirent' cloning. > > > > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/841 > > Cc: qemu-stable@nongnu.org > > Co-authored-by: Christian Schoenebeck <qemu_oss@crudebyte.com> > > Reviewed-by: Dmitry V. Levin <ldv@altlinux.org> > > Signed-off-by: Vitaly Chikunov <vt@altlinux.org> > > --- > > Tested on x68-64 Linux with btrfs-progs tests and qos-test -m slow. > > Consider donating your Tested-by tag then. > > > Changes since v4: > > - Zero clear V9fsSynthOpenState on allocation. Uninitialised use of > > d_reclen bug found by fuzzing. Use g_new0 instead of g_malloc0 as > > Greg Kurz suggested. > > I can confirm that v4 triggered the previously discussed ASan error when > running the 9p 'synth' tests; and with this v5 ASan no longer triggers an > error. > > Tested-by: Christian Schoenebeck <qemu_oss@crudebyte.com> Tested-by: Vitaly Chikunov <vt@altlinux.org> > > Maybe some of the new comments could be improved, for instance ... > > > > > hw/9pfs/9p-synth.c | 18 +++++++++++++++--- > > hw/9pfs/9p-synth.h | 5 +++++ > > hw/9pfs/codir.c | 3 +-- > > include/qemu/osdep.h | 13 +++++++++++++ > > util/osdep.c | 21 +++++++++++++++++++++ > > 5 files changed, 55 insertions(+), 5 deletions(-) > > > > diff --git a/hw/9pfs/9p-synth.c b/hw/9pfs/9p-synth.c > > index b38088e066..396cda36f1 100644 > > --- a/hw/9pfs/9p-synth.c > > +++ b/hw/9pfs/9p-synth.c > > @@ -182,7 +182,12 @@ static int synth_opendir(FsContext *ctx, > > V9fsSynthOpenState *synth_open; > > V9fsSynthNode *node = *(V9fsSynthNode **)fs_path->data; > > > > - synth_open = g_malloc(sizeof(*synth_open)); > > + /* > > + * V9fsSynthOpenState contains 'struct dirent' which have OS-specific > > + * properties, thus it's zero cleared on allocation here and below > > + * in synth_open. > > + */ > > + synth_open = g_new0(V9fsSynthOpenState, 1); > > synth_open->node = node; > > node->open_count++; > > fs->private = synth_open; > > @@ -220,7 +225,14 @@ static void synth_rewinddir(FsContext *ctx, > > V9fsFidOpenState *fs) static void synth_direntry(V9fsSynthNode *node, > > struct dirent *entry, off_t off) > > { > > - strcpy(entry->d_name, node->name); > > + size_t sz = strlen(node->name) + 1; > > + /* > > + * 'entry' is always inside of V9fsSynthOpenState which have NAME_MAX > > + * back padding. Ensure we do not orerflow it. > > + */ > > ... here is a typo in the comment. But unless there are more issues, I could > handle such minor comment issues on my end before pushing. Ah, thanks! Vitaly, > > Reviewed-by: Christian Schoenebeck <qemu_oss@crudebyte.com> > > Best regards, > Christian Schoenebeck > > > + g_assert(sizeof(struct dirent) + NAME_MAX >= > > + offsetof(struct dirent, d_name) + sz); > > + memcpy(entry->d_name, node->name, sz); > > entry->d_ino = node->attr->inode; > > entry->d_off = off + 1; > > } > > @@ -266,7 +278,7 @@ static int synth_open(FsContext *ctx, V9fsPath *fs_path, > > V9fsSynthOpenState *synth_open; > > V9fsSynthNode *node = *(V9fsSynthNode **)fs_path->data; > > > > - synth_open = g_malloc(sizeof(*synth_open)); > > + synth_open = g_new0(V9fsSynthOpenState, 1); > > synth_open->node = node; > > node->open_count++; > > fs->private = synth_open; > > diff --git a/hw/9pfs/9p-synth.h b/hw/9pfs/9p-synth.h > > index 036d7e4a5b..eeb246f377 100644 > > --- a/hw/9pfs/9p-synth.h > > +++ b/hw/9pfs/9p-synth.h > > @@ -41,6 +41,11 @@ typedef struct V9fsSynthOpenState { > > off_t offset; > > V9fsSynthNode *node; > > struct dirent dent; > > + /* > > + * Ensure there is enough space for 'dent' above, some systems have a > > + * d_name size of just 1, which would cause a buffer overrun. > > + */ > > + char dent_trailing_space[NAME_MAX]; > > } V9fsSynthOpenState; > > > > int qemu_v9fs_synth_mkdir(V9fsSynthNode *parent, int mode, > > diff --git a/hw/9pfs/codir.c b/hw/9pfs/codir.c > > index 032cce04c4..c0873bde16 100644 > > --- a/hw/9pfs/codir.c > > +++ b/hw/9pfs/codir.c > > @@ -143,8 +143,7 @@ static int do_readdir_many(V9fsPDU *pdu, V9fsFidState > > *fidp, } else { > > e = e->next = g_malloc0(sizeof(V9fsDirEnt)); > > } > > - e->dent = g_malloc0(sizeof(struct dirent)); > > - memcpy(e->dent, dent, sizeof(struct dirent)); > > + e->dent = qemu_dirent_dup(dent); > > > > /* perform a full stat() for directory entry if requested by caller > > */ if (dostat) { > > diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h > > index d1660d67fa..ce12f64853 100644 > > --- a/include/qemu/osdep.h > > +++ b/include/qemu/osdep.h > > @@ -805,6 +805,19 @@ static inline int > > platform_does_not_support_system(const char *command) } > > #endif /* !HAVE_SYSTEM_FUNCTION */ > > > > +/** > > + * Duplicate directory entry @dent. > > + * > > + * It is highly recommended to use this function instead of open coding > > + * duplication of @c dirent objects, because the actual @c struct @c dirent > > + * size may be bigger or shorter than @c sizeof(struct dirent) and correct > > + * handling is platform specific (see gitlab issue #841). > > + * > > + * @dent - original directory entry to be duplicated > > + * @returns duplicated directory entry which should be freed with g_free() > > + */ > > +struct dirent *qemu_dirent_dup(struct dirent *dent); > > + > > #ifdef __cplusplus > > } > > #endif > > diff --git a/util/osdep.c b/util/osdep.c > > index 42a0a4986a..67fbf22778 100644 > > --- a/util/osdep.c > > +++ b/util/osdep.c > > @@ -33,6 +33,7 @@ > > extern int madvise(char *, size_t, int); > > #endif > > > > +#include <dirent.h> > > #include "qemu-common.h" > > #include "qemu/cutils.h" > > #include "qemu/sockets.h" > > @@ -615,3 +616,23 @@ writev(int fd, const struct iovec *iov, int iov_cnt) > > return readv_writev(fd, iov, iov_cnt, true); > > } > > #endif > > + > > +struct dirent * > > +qemu_dirent_dup(struct dirent *dent) > > +{ > > + size_t sz = 0; > > +#if defined _DIRENT_HAVE_D_RECLEN > > + /* Avoid use of strlen() if platform supports d_reclen. */ > > + sz = dent->d_reclen; > > +#endif > > + /* > > + * Test sz for zero even if d_reclen is available > > + * because some drivers may set d_reclen to zero. > > + */ > > + if (sz == 0) { > > + /* Fallback to the most portable way. */ > > + sz = offsetof(struct dirent, d_name) + > > + strlen(dent->d_name) + 1; > > + } > > + return g_memdup(dent, sz); > > +} >
On Mittwoch, 16. Februar 2022 19:18:21 CET Vitaly Chikunov wrote: > `struct dirent' returned from readdir(3) could be shorter (or longer) > than `sizeof(struct dirent)', thus memcpy of sizeof length will overread > into unallocated page causing SIGSEGV. Example stack trace: > > #0 0x00005555559ebeed v9fs_co_readdir_many (/usr/bin/qemu-system-x86_64 + > 0x497eed) #1 0x00005555559ec2e9 v9fs_readdir (/usr/bin/qemu-system-x86_64 > + 0x4982e9) #2 0x0000555555eb7983 coroutine_trampoline > (/usr/bin/qemu-system-x86_64 + 0x963983) #3 0x00007ffff73e0be0 n/a (n/a + > 0x0) > > While fixing this, provide a helper for any future `struct dirent' cloning. > > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/841 > Cc: qemu-stable@nongnu.org > Co-authored-by: Christian Schoenebeck <qemu_oss@crudebyte.com> > Reviewed-by: Dmitry V. Levin <ldv@altlinux.org> > Signed-off-by: Vitaly Chikunov <vt@altlinux.org> > --- Queued on 9p.next: https://github.com/cschoenebeck/qemu/commits/9p.next Thanks! I prepare a new PR now. Best regards, Christian Schoenebeck
On Wed, 16 Feb 2022 21:18:21 +0300 Vitaly Chikunov <vt@altlinux.org> wrote: > `struct dirent' returned from readdir(3) could be shorter (or longer) > than `sizeof(struct dirent)', thus memcpy of sizeof length will overread > into unallocated page causing SIGSEGV. Example stack trace: > > #0 0x00005555559ebeed v9fs_co_readdir_many (/usr/bin/qemu-system-x86_64 + 0x497eed) > #1 0x00005555559ec2e9 v9fs_readdir (/usr/bin/qemu-system-x86_64 + 0x4982e9) > #2 0x0000555555eb7983 coroutine_trampoline (/usr/bin/qemu-system-x86_64 + 0x963983) > #3 0x00007ffff73e0be0 n/a (n/a + 0x0) > > While fixing this, provide a helper for any future `struct dirent' cloning. > > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/841 > Cc: qemu-stable@nongnu.org > Co-authored-by: Christian Schoenebeck <qemu_oss@crudebyte.com> > Reviewed-by: Dmitry V. Levin <ldv@altlinux.org> > Signed-off-by: Vitaly Chikunov <vt@altlinux.org> > --- > Tested on x68-64 Linux with btrfs-progs tests and qos-test -m slow. > Changes since v4: > - Zero clear V9fsSynthOpenState on allocation. Uninitialised use of > d_reclen bug found by fuzzing. Use g_new0 instead of g_malloc0 as > Greg Kurz suggested. > The synth fixes would have deserved a separate patch and I'm not super fan of the padding hack... I'd rather allocate the dirent dynamically with the right size and populated according to the _DIRENT_HAVE macros. Anyway, this fix should be enough for now and Christian already provided his R-b, so: Acked-by: Greg Kurz <groug@kaod.org> > hw/9pfs/9p-synth.c | 18 +++++++++++++++--- > hw/9pfs/9p-synth.h | 5 +++++ > hw/9pfs/codir.c | 3 +-- > include/qemu/osdep.h | 13 +++++++++++++ > util/osdep.c | 21 +++++++++++++++++++++ > 5 files changed, 55 insertions(+), 5 deletions(-) > > diff --git a/hw/9pfs/9p-synth.c b/hw/9pfs/9p-synth.c > index b38088e066..396cda36f1 100644 > --- a/hw/9pfs/9p-synth.c > +++ b/hw/9pfs/9p-synth.c > @@ -182,7 +182,12 @@ static int synth_opendir(FsContext *ctx, > V9fsSynthOpenState *synth_open; > V9fsSynthNode *node = *(V9fsSynthNode **)fs_path->data; > > - synth_open = g_malloc(sizeof(*synth_open)); > + /* > + * V9fsSynthOpenState contains 'struct dirent' which have OS-specific > + * properties, thus it's zero cleared on allocation here and below > + * in synth_open. > + */ > + synth_open = g_new0(V9fsSynthOpenState, 1); > synth_open->node = node; > node->open_count++; > fs->private = synth_open; > @@ -220,7 +225,14 @@ static void synth_rewinddir(FsContext *ctx, V9fsFidOpenState *fs) > static void synth_direntry(V9fsSynthNode *node, > struct dirent *entry, off_t off) > { > - strcpy(entry->d_name, node->name); > + size_t sz = strlen(node->name) + 1; > + /* > + * 'entry' is always inside of V9fsSynthOpenState which have NAME_MAX > + * back padding. Ensure we do not orerflow it. > + */ > + g_assert(sizeof(struct dirent) + NAME_MAX >= > + offsetof(struct dirent, d_name) + sz); > + memcpy(entry->d_name, node->name, sz); > entry->d_ino = node->attr->inode; > entry->d_off = off + 1; > } > @@ -266,7 +278,7 @@ static int synth_open(FsContext *ctx, V9fsPath *fs_path, > V9fsSynthOpenState *synth_open; > V9fsSynthNode *node = *(V9fsSynthNode **)fs_path->data; > > - synth_open = g_malloc(sizeof(*synth_open)); > + synth_open = g_new0(V9fsSynthOpenState, 1); > synth_open->node = node; > node->open_count++; > fs->private = synth_open; > diff --git a/hw/9pfs/9p-synth.h b/hw/9pfs/9p-synth.h > index 036d7e4a5b..eeb246f377 100644 > --- a/hw/9pfs/9p-synth.h > +++ b/hw/9pfs/9p-synth.h > @@ -41,6 +41,11 @@ typedef struct V9fsSynthOpenState { > off_t offset; > V9fsSynthNode *node; > struct dirent dent; > + /* > + * Ensure there is enough space for 'dent' above, some systems have a > + * d_name size of just 1, which would cause a buffer overrun. > + */ > + char dent_trailing_space[NAME_MAX]; > } V9fsSynthOpenState; > > int qemu_v9fs_synth_mkdir(V9fsSynthNode *parent, int mode, > diff --git a/hw/9pfs/codir.c b/hw/9pfs/codir.c > index 032cce04c4..c0873bde16 100644 > --- a/hw/9pfs/codir.c > +++ b/hw/9pfs/codir.c > @@ -143,8 +143,7 @@ static int do_readdir_many(V9fsPDU *pdu, V9fsFidState *fidp, > } else { > e = e->next = g_malloc0(sizeof(V9fsDirEnt)); > } > - e->dent = g_malloc0(sizeof(struct dirent)); > - memcpy(e->dent, dent, sizeof(struct dirent)); > + e->dent = qemu_dirent_dup(dent); > > /* perform a full stat() for directory entry if requested by caller */ > if (dostat) { > diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h > index d1660d67fa..ce12f64853 100644 > --- a/include/qemu/osdep.h > +++ b/include/qemu/osdep.h > @@ -805,6 +805,19 @@ static inline int platform_does_not_support_system(const char *command) > } > #endif /* !HAVE_SYSTEM_FUNCTION */ > > +/** > + * Duplicate directory entry @dent. > + * > + * It is highly recommended to use this function instead of open coding > + * duplication of @c dirent objects, because the actual @c struct @c dirent > + * size may be bigger or shorter than @c sizeof(struct dirent) and correct > + * handling is platform specific (see gitlab issue #841). > + * > + * @dent - original directory entry to be duplicated > + * @returns duplicated directory entry which should be freed with g_free() > + */ > +struct dirent *qemu_dirent_dup(struct dirent *dent); > + > #ifdef __cplusplus > } > #endif > diff --git a/util/osdep.c b/util/osdep.c > index 42a0a4986a..67fbf22778 100644 > --- a/util/osdep.c > +++ b/util/osdep.c > @@ -33,6 +33,7 @@ > extern int madvise(char *, size_t, int); > #endif > > +#include <dirent.h> > #include "qemu-common.h" > #include "qemu/cutils.h" > #include "qemu/sockets.h" > @@ -615,3 +616,23 @@ writev(int fd, const struct iovec *iov, int iov_cnt) > return readv_writev(fd, iov, iov_cnt, true); > } > #endif > + > +struct dirent * > +qemu_dirent_dup(struct dirent *dent) > +{ > + size_t sz = 0; > +#if defined _DIRENT_HAVE_D_RECLEN > + /* Avoid use of strlen() if platform supports d_reclen. */ > + sz = dent->d_reclen; > +#endif > + /* > + * Test sz for zero even if d_reclen is available > + * because some drivers may set d_reclen to zero. > + */ > + if (sz == 0) { > + /* Fallback to the most portable way. */ > + sz = offsetof(struct dirent, d_name) + > + strlen(dent->d_name) + 1; > + } > + return g_memdup(dent, sz); > +}
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