hw/9pfs/codir.c | 7 +++++-- include/qemu/osdep.h | 6 ++++++ util/osdep.c | 23 +++++++++++++++++++++++ 3 files changed, 34 insertions(+), 2 deletions(-)
`struct dirent' returned from readdir(3) could be shorter 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)
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/841
Signed-off-by: Vitaly Chikunov <vt@altlinux.org>
---
Tested on x86-64 Linux.
hw/9pfs/codir.c | 7 +++++--
include/qemu/osdep.h | 6 ++++++
util/osdep.c | 23 +++++++++++++++++++++++
3 files changed, 34 insertions(+), 2 deletions(-)
diff --git a/hw/9pfs/codir.c b/hw/9pfs/codir.c
index 032cce04c4..ea7f5e6578 100644
--- a/hw/9pfs/codir.c
+++ b/hw/9pfs/codir.c
@@ -143,8 +143,11 @@ 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);
+ if (!e->dent) {
+ err = -errno;
+ break;
+ }
/* 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..b54d22db04 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -805,6 +805,12 @@ static inline int platform_does_not_support_system(const char *command)
}
#endif /* !HAVE_SYSTEM_FUNCTION */
+/**
+ * Actual 'struct dirent' size may be bigger or shorter than
+ * sizeof(struct dirent) in many cases.
+ */
+struct dirent *qemu_dirent_dup(struct dirent *dent);
+
#ifdef __cplusplus
}
#endif
diff --git a/util/osdep.c b/util/osdep.c
index 42a0a4986a..e39d1071fd 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 +616,25 @@ 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)
+{
+ struct dirent *dst;
+#if defined _DIRENT_HAVE_D_RECLEN
+ /* Avoid use of strlen() if there's d_reclen. */
+ dst = g_malloc(dent->d_reclen);
+#else
+ /* Fallback to a most portable way. */
+ const size_t reclen = offsetof(struct dirent, d_name) + strlen(dent->d_name) + 1;
+
+ dst = g_malloc(reclen);
+#endif
+ if (!dst)
+ return NULL;
+#ifdef _DIRENT_HAVE_D_RECLEN
+ return memcpy(dst, dent, dent->d_reclen);
+#else
+ return memcpy(dst, dent, reclen);
+#endif
+}
--
2.33.0
On Donnerstag, 27. Januar 2022 22:27:34 CET Vitaly Chikunov wrote:
> `struct dirent' returned from readdir(3) could be shorter than
> `sizeof(struct dirent)', thus memcpy of sizeof length will overread
> into unallocated page causing SIGSEGV. Example stack trace:
It could be shorter or longer. Your patch is fixing both possibilities.
I just realized BTW that there are other places that should be fixed as well.
:/
For instance hw/9pfs/9p-synth.c (used for the 9p test cases [1][2]) is copying
dirents, too.
And in hw/9pfs/9p.c v9fs_do_readdir_with_stat() used by 9p2000.u doesn't even
bother to copy at all, which is undefined behaviour as fs driver is running on
a background thread and the dirent pointer might have mutated in the meantime
with the next readdir() call.
[1] https://wiki.qemu.org/Documentation/9p#Test_Cases
[2] https://wiki.qemu.org/Documentation/9p#9p_Filesystem_Drivers
> #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)
>
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/841
> Signed-off-by: Vitaly Chikunov <vt@altlinux.org>
Adding qemu-stable on CC for making sure this patch will be handled for the
stable branches as well.
> ---
> Tested on x86-64 Linux.
>
> hw/9pfs/codir.c | 7 +++++--
> include/qemu/osdep.h | 6 ++++++
> util/osdep.c | 23 +++++++++++++++++++++++
> 3 files changed, 34 insertions(+), 2 deletions(-)
>
> diff --git a/hw/9pfs/codir.c b/hw/9pfs/codir.c
> index 032cce04c4..ea7f5e6578 100644
> --- a/hw/9pfs/codir.c
> +++ b/hw/9pfs/codir.c
> @@ -143,8 +143,11 @@ 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);
That's the actual fix.
> + if (!e->dent) {
> + err = -errno;
> + break;
> + }
e->dent is never NULL, so this check can be removed. See explanation about
g_malloc() below.
>
> /* 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..b54d22db04 100644
> --- a/include/qemu/osdep.h
> +++ b/include/qemu/osdep.h
> @@ -805,6 +805,12 @@ static inline int
> platform_does_not_support_system(const char *command) }
> #endif /* !HAVE_SYSTEM_FUNCTION */
>
> +/**
> + * Actual 'struct dirent' size may be bigger or shorter than
> + * sizeof(struct dirent) in many cases.
> + */
> +struct dirent *qemu_dirent_dup(struct dirent *dent);
> +
I think this issue deserves a more verbose API doc comment, something like:
/**
* 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..e39d1071fd 100644
> --- a/util/osdep.c
> +++ b/util/osdep.c
> @@ -33,6 +33,7 @@
> extern int madvise(char *, size_t, int);
> #endif
>
> +#include <dirent.h>
Wouldn't that break Windows builds?
> #include "qemu-common.h"
> #include "qemu/cutils.h"
> #include "qemu/sockets.h"
> @@ -615,3 +616,25 @@ 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)
> +{
> + struct dirent *dst;
> +#if defined _DIRENT_HAVE_D_RECLEN
> + /* Avoid use of strlen() if there's d_reclen. */
> + dst = g_malloc(dent->d_reclen);
> +#else
> + /* Fallback to a most portable way. */
> + const size_t reclen = offsetof(struct dirent, d_name) +
> strlen(dent->d_name) + 1; +
> + dst = g_malloc(reclen);
> +#endif
> + if (!dst)
> + return NULL;
> +#ifdef _DIRENT_HAVE_D_RECLEN
> + return memcpy(dst, dent, dent->d_reclen);
> +#else
> + return memcpy(dst, dent, reclen);
> +#endif
> +}
On the long run we probably should have a configure check whether d_reclen
exists, but I would not insist on that now as there is a valid fallback
solution at least.
Note that g_malloc() never returns NULL, if it runs out of memory it
terminates instead, so the NULL checks are unncessary:
https://developer.gimp.org/api/2.0/glib/glib-Memory-Allocation.html#g-try-malloc
Also I would prefer g_malloc0() over g_malloc().
Then by adding a variable for the d_reclen yes/no case, overall code can be
reduced. So I would suggest something like this instead:
struct dirent *
qemu_dirent_dup(struct dirent *dent)
{
#if defined _DIRENT_HAVE_D_RECLEN
/* Avoid use of strlen() if there's d_reclen. */
const size_t sz = dent->d_reclen;
#else
/* Fallback to a most portable way. */
const size_t sz = offsetof(struct dirent, d_name) +
strlen(dent->d_name) + 1;
#endif
struct dirent *dst = g_malloc(sz);
return memcpy(dst, dent, sz);
}
Best regards,
Christian Schoenebeck
On Freitag, 28. Januar 2022 15:43:10 CET Christian Schoenebeck wrote:
> Also I would prefer g_malloc0() over g_malloc().
Never mind about that one. g_malloc0() with immediate subsequent memcpy() and
exact same size argument would be pointless.
> Then by adding a variable for the d_reclen yes/no case, overall code can be
> reduced. So I would suggest something like this instead:
>
> struct dirent *
> qemu_dirent_dup(struct dirent *dent)
> {
> #if defined _DIRENT_HAVE_D_RECLEN
> /* Avoid use of strlen() if there's d_reclen. */
> const size_t sz = dent->d_reclen;
> #else
> /* Fallback to a most portable way. */
> const size_t sz = offsetof(struct dirent, d_name) +
> strlen(dent->d_name) + 1;
> #endif
> struct dirent *dst = g_malloc(sz);
> return memcpy(dst, dent, sz);
> }
Best regards,
Christian Schoenebeck
Christian,
On Fri, Jan 28, 2022 at 03:43:10PM +0100, Christian Schoenebeck wrote:
> On Donnerstag, 27. Januar 2022 22:27:34 CET Vitaly Chikunov wrote:
> > `struct dirent' returned from readdir(3) could be shorter than
> > `sizeof(struct dirent)', thus memcpy of sizeof length will overread
> > into unallocated page causing SIGSEGV. Example stack trace:
>
> It could be shorter or longer. Your patch is fixing both possibilities.
>
> I just realized BTW that there are other places that should be fixed as well.
> :/
>
> For instance hw/9pfs/9p-synth.c (used for the 9p test cases [1][2]) is copying
> dirents, too.
I noticed this one too, it could theoretically result in overflow on
CIFS if long filenames are prepared. But I decided to concentrate on
this more important fix, since this happen on normal fs.
I will apply all other your comments, except these new fixes.
> And in hw/9pfs/9p.c v9fs_do_readdir_with_stat() used by 9p2000.u doesn't even
> bother to copy at all, which is undefined behaviour as fs driver is running on
> a background thread and the dirent pointer might have mutated in the meantime
> with the next readdir() call.
>
> [1] https://wiki.qemu.org/Documentation/9p#Test_Cases
> [2] https://wiki.qemu.org/Documentation/9p#9p_Filesystem_Drivers
>
> > #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)
> >
> > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/841
> > Signed-off-by: Vitaly Chikunov <vt@altlinux.org>
>
> Adding qemu-stable on CC for making sure this patch will be handled for the
> stable branches as well.
>
> > ---
> > Tested on x86-64 Linux.
> >
> > hw/9pfs/codir.c | 7 +++++--
> > include/qemu/osdep.h | 6 ++++++
> > util/osdep.c | 23 +++++++++++++++++++++++
> > 3 files changed, 34 insertions(+), 2 deletions(-)
> >
> > diff --git a/hw/9pfs/codir.c b/hw/9pfs/codir.c
> > index 032cce04c4..ea7f5e6578 100644
> > --- a/hw/9pfs/codir.c
> > +++ b/hw/9pfs/codir.c
> > @@ -143,8 +143,11 @@ 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);
>
> That's the actual fix.
>
> > + if (!e->dent) {
> > + err = -errno;
> > + break;
> > + }
>
> e->dent is never NULL, so this check can be removed. See explanation about
> g_malloc() below.
Yes, I forgot about this.
> >
> > /* 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..b54d22db04 100644
> > --- a/include/qemu/osdep.h
> > +++ b/include/qemu/osdep.h
> > @@ -805,6 +805,12 @@ static inline int
> > platform_does_not_support_system(const char *command) }
> > #endif /* !HAVE_SYSTEM_FUNCTION */
> >
> > +/**
> > + * Actual 'struct dirent' size may be bigger or shorter than
> > + * sizeof(struct dirent) in many cases.
> > + */
> > +struct dirent *qemu_dirent_dup(struct dirent *dent);
> > +
>
> I think this issue deserves a more verbose API doc comment, something like:
>
> /**
> * 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..e39d1071fd 100644
> > --- a/util/osdep.c
> > +++ b/util/osdep.c
> > @@ -33,6 +33,7 @@
> > extern int madvise(char *, size_t, int);
> > #endif
> >
> > +#include <dirent.h>
>
> Wouldn't that break Windows builds?
Possible, but I don't have windows build to test. What would you
suggest as better fix?
I took as example `util/path.c' which includes `dirent.h' too, but it is
not handled anyway different than `util/osdep.c'
>
> > #include "qemu-common.h"
> > #include "qemu/cutils.h"
> > #include "qemu/sockets.h"
> > @@ -615,3 +616,25 @@ 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)
> > +{
> > + struct dirent *dst;
> > +#if defined _DIRENT_HAVE_D_RECLEN
> > + /* Avoid use of strlen() if there's d_reclen. */
> > + dst = g_malloc(dent->d_reclen);
> > +#else
> > + /* Fallback to a most portable way. */
> > + const size_t reclen = offsetof(struct dirent, d_name) +
> > strlen(dent->d_name) + 1; +
> > + dst = g_malloc(reclen);
> > +#endif
> > + if (!dst)
> > + return NULL;
> > +#ifdef _DIRENT_HAVE_D_RECLEN
> > + return memcpy(dst, dent, dent->d_reclen);
> > +#else
> > + return memcpy(dst, dent, reclen);
> > +#endif
> > +}
>
> On the long run we probably should have a configure check whether d_reclen
> exists, but I would not insist on that now as there is a valid fallback
> solution at least.
>
> Note that g_malloc() never returns NULL, if it runs out of memory it
> terminates instead, so the NULL checks are unncessary:
> https://developer.gimp.org/api/2.0/glib/glib-Memory-Allocation.html#g-try-malloc
>
> Also I would prefer g_malloc0() over g_malloc().
>
> Then by adding a variable for the d_reclen yes/no case, overall code can be
> reduced. So I would suggest something like this instead:
>
> struct dirent *
> qemu_dirent_dup(struct dirent *dent)
> {
> #if defined _DIRENT_HAVE_D_RECLEN
> /* Avoid use of strlen() if there's d_reclen. */
> const size_t sz = dent->d_reclen;
> #else
> /* Fallback to a most portable way. */
> const size_t sz = offsetof(struct dirent, d_name) +
> strlen(dent->d_name) + 1;
> #endif
> struct dirent *dst = g_malloc(sz);
> return memcpy(dst, dent, sz);
> }
>
> Best regards,
> Christian Schoenebeck
Thanks!
>
On Freitag, 28. Januar 2022 17:24:01 CET Vitaly Chikunov wrote: > > > diff --git a/util/osdep.c b/util/osdep.c > > > index 42a0a4986a..e39d1071fd 100644 > > > --- a/util/osdep.c > > > +++ b/util/osdep.c > > > @@ -33,6 +33,7 @@ > > > > > > extern int madvise(char *, size_t, int); > > > #endif > > > > > > +#include <dirent.h> > > > > Wouldn't that break Windows builds? > > Possible, but I don't have windows build to test. What would you > suggest as better fix? > > I took as example `util/path.c' which includes `dirent.h' too, but it is > not handled anyway different than `util/osdep.c' AFAICS the current expectation is to build QEMU for Windows with a POSIX-aware toolchain like msys2, cygwin or some cross compiler: https://wiki.qemu.org/Hosts/W32 So I suggest leave it as is, it should be fine. Otherwise we can still wrap it into something like #if !defined(WIN32) ... #endif later on if really required. Best regards, Christian Schoenebeck
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