linux-user/main.c | 6 ++++++ linux-user/syscall.c | 34 ++++++++++------------------------ 2 files changed, 16 insertions(+), 24 deletions(-)
When accsssing /proc/self/exe from a userspace program, linux-user tries
to resolve the name via realpath(), which may fail if the process
changed the working directory in the meantime.
An example:
- a userspace program ist started with ./testprogram
- the program runs chdir("/tmp")
- then the program calls readlink("/proc/self/exe")
- linux-user tries to run realpath("./testprogram") which fails
because ./testprogram isn't in /tmp
- readlink() will return -ENOENT back to the program
Avoid this issue by resolving the full path name of the started process
at startup of linux-user and store it in real_exec_path[]. This then
simplifies the emulation of readlink() and readlinkat() as well, because
they can simply copy the path string to userspace.
I noticed this bug because the testsuite of the debian package "pandoc"
failed on linux-user while it succeeded on real hardware. The full log
is here:
https://buildd.debian.org/status/fetch.php?pkg=pandoc&arch=hppa&ver=2.17.1.1-1.1%2Bb1&stamp=1670153210&raw=0
Signed-off-by: Helge Deller <deller@gmx.de>
---
linux-user/main.c | 6 ++++++
linux-user/syscall.c | 34 ++++++++++------------------------
2 files changed, 16 insertions(+), 24 deletions(-)
diff --git a/linux-user/main.c b/linux-user/main.c
index aedd707459..e7e53f7d5e 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -64,6 +64,7 @@
#endif
char *exec_path;
+char real_exec_path[PATH_MAX];
int singlestep;
static const char *argv0;
@@ -744,6 +745,11 @@ int main(int argc, char **argv, char **envp)
}
}
+ /* Resolve executable file name to full path name */
+ if (realpath(exec_path, real_exec_path)) {
+ exec_path = real_exec_path;
+ }
+
/*
* get binfmt_misc flags
* but only if not already done by parse_args() above
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 0468a1bad7..71ae867024 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -10011,18 +10011,11 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int num, abi_long arg1,
/* Short circuit this for the magic exe check. */
ret = -TARGET_EINVAL;
} else if (is_proc_myself((const char *)p, "exe")) {
- char real[PATH_MAX], *temp;
- temp = realpath(exec_path, real);
- /* Return value is # of bytes that we wrote to the buffer. */
- if (temp == NULL) {
- ret = get_errno(-1);
- } else {
- /* Don't worry about sign mismatch as earlier mapping
- * logic would have thrown a bad address error. */
- ret = MIN(strlen(real), arg3);
- /* We cannot NUL terminate the string. */
- memcpy(p2, real, ret);
- }
+ /* Don't worry about sign mismatch as earlier mapping
+ * logic would have thrown a bad address error. */
+ ret = MIN(strlen(exec_path), arg3);
+ /* We cannot NUL terminate the string. */
+ memcpy(p2, exec_path, ret);
} else {
ret = get_errno(readlink(path(p), p2, arg3));
}
@@ -10043,18 +10036,11 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int num, abi_long arg1,
/* Short circuit this for the magic exe check. */
ret = -TARGET_EINVAL;
} else if (is_proc_myself((const char *)p, "exe")) {
- char real[PATH_MAX], *temp;
- temp = realpath(exec_path, real);
- /* Return value is # of bytes that we wrote to the buffer. */
- if (temp == NULL) {
- ret = get_errno(-1);
- } else {
- /* Don't worry about sign mismatch as earlier mapping
- * logic would have thrown a bad address error. */
- ret = MIN(strlen(real), arg4);
- /* We cannot NUL terminate the string. */
- memcpy(p2, real, ret);
- }
+ /* Don't worry about sign mismatch as earlier mapping
+ * logic would have thrown a bad address error. */
+ ret = MIN(strlen(exec_path), arg4);
+ /* We cannot NUL terminate the string. */
+ memcpy(p2, exec_path, ret);
} else {
ret = get_errno(readlinkat(arg1, path(p), p2, arg4));
}
--
2.38.1
Le 05/12/2022 à 12:38, Helge Deller a écrit : > When accsssing /proc/self/exe from a userspace program, linux-user tries > to resolve the name via realpath(), which may fail if the process > changed the working directory in the meantime. > > An example: > - a userspace program ist started with ./testprogram > - the program runs chdir("/tmp") > - then the program calls readlink("/proc/self/exe") > - linux-user tries to run realpath("./testprogram") which fails > because ./testprogram isn't in /tmp > - readlink() will return -ENOENT back to the program > > Avoid this issue by resolving the full path name of the started process > at startup of linux-user and store it in real_exec_path[]. This then > simplifies the emulation of readlink() and readlinkat() as well, because > they can simply copy the path string to userspace. > > I noticed this bug because the testsuite of the debian package "pandoc" > failed on linux-user while it succeeded on real hardware. The full log > is here: > https://buildd.debian.org/status/fetch.php?pkg=pandoc&arch=hppa&ver=2.17.1.1-1.1%2Bb1&stamp=1670153210&raw=0 > > Signed-off-by: Helge Deller <deller@gmx.de> > --- > linux-user/main.c | 6 ++++++ > linux-user/syscall.c | 34 ++++++++++------------------------ > 2 files changed, 16 insertions(+), 24 deletions(-) > > diff --git a/linux-user/main.c b/linux-user/main.c > index aedd707459..e7e53f7d5e 100644 > --- a/linux-user/main.c > +++ b/linux-user/main.c > @@ -64,6 +64,7 @@ > #endif > > char *exec_path; > +char real_exec_path[PATH_MAX]; > > int singlestep; > static const char *argv0; > @@ -744,6 +745,11 @@ int main(int argc, char **argv, char **envp) > } > } > > + /* Resolve executable file name to full path name */ > + if (realpath(exec_path, real_exec_path)) { > + exec_path = real_exec_path; > + } > + > /* > * get binfmt_misc flags > * but only if not already done by parse_args() above > diff --git a/linux-user/syscall.c b/linux-user/syscall.c > index 0468a1bad7..71ae867024 100644 > --- a/linux-user/syscall.c > +++ b/linux-user/syscall.c > @@ -10011,18 +10011,11 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int num, abi_long arg1, > /* Short circuit this for the magic exe check. */ > ret = -TARGET_EINVAL; > } else if (is_proc_myself((const char *)p, "exe")) { > - char real[PATH_MAX], *temp; > - temp = realpath(exec_path, real); > - /* Return value is # of bytes that we wrote to the buffer. */ > - if (temp == NULL) { > - ret = get_errno(-1); > - } else { > - /* Don't worry about sign mismatch as earlier mapping > - * logic would have thrown a bad address error. */ > - ret = MIN(strlen(real), arg3); > - /* We cannot NUL terminate the string. */ > - memcpy(p2, real, ret); > - } > + /* Don't worry about sign mismatch as earlier mapping > + * logic would have thrown a bad address error. */ > + ret = MIN(strlen(exec_path), arg3); > + /* We cannot NUL terminate the string. */ > + memcpy(p2, exec_path, ret); > } else { > ret = get_errno(readlink(path(p), p2, arg3)); > } > @@ -10043,18 +10036,11 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int num, abi_long arg1, > /* Short circuit this for the magic exe check. */ > ret = -TARGET_EINVAL; > } else if (is_proc_myself((const char *)p, "exe")) { > - char real[PATH_MAX], *temp; > - temp = realpath(exec_path, real); > - /* Return value is # of bytes that we wrote to the buffer. */ > - if (temp == NULL) { > - ret = get_errno(-1); > - } else { > - /* Don't worry about sign mismatch as earlier mapping > - * logic would have thrown a bad address error. */ > - ret = MIN(strlen(real), arg4); > - /* We cannot NUL terminate the string. */ > - memcpy(p2, real, ret); > - } > + /* Don't worry about sign mismatch as earlier mapping > + * logic would have thrown a bad address error. */ > + ret = MIN(strlen(exec_path), arg4); > + /* We cannot NUL terminate the string. */ > + memcpy(p2, exec_path, ret); > } else { > ret = get_errno(readlinkat(arg1, path(p), p2, arg4)); > } > -- > 2.38.1 > > Applied to my linux-user-for-8.0 branch. Thanks, Laurent
Le 05/12/2022 à 12:38, Helge Deller a écrit : > When accsssing /proc/self/exe from a userspace program, linux-user tries > to resolve the name via realpath(), which may fail if the process > changed the working directory in the meantime. > > An example: > - a userspace program ist started with ./testprogram > - the program runs chdir("/tmp") > - then the program calls readlink("/proc/self/exe") > - linux-user tries to run realpath("./testprogram") which fails > because ./testprogram isn't in /tmp > - readlink() will return -ENOENT back to the program > > Avoid this issue by resolving the full path name of the started process > at startup of linux-user and store it in real_exec_path[]. This then > simplifies the emulation of readlink() and readlinkat() as well, because > they can simply copy the path string to userspace. > > I noticed this bug because the testsuite of the debian package "pandoc" > failed on linux-user while it succeeded on real hardware. The full log > is here: > https://buildd.debian.org/status/fetch.php?pkg=pandoc&arch=hppa&ver=2.17.1.1-1.1%2Bb1&stamp=1670153210&raw=0 > > Signed-off-by: Helge Deller <deller@gmx.de> > --- > linux-user/main.c | 6 ++++++ > linux-user/syscall.c | 34 ++++++++++------------------------ > 2 files changed, 16 insertions(+), 24 deletions(-) > > diff --git a/linux-user/main.c b/linux-user/main.c > index aedd707459..e7e53f7d5e 100644 > --- a/linux-user/main.c > +++ b/linux-user/main.c > @@ -64,6 +64,7 @@ > #endif > > char *exec_path; > +char real_exec_path[PATH_MAX]; > > int singlestep; > static const char *argv0; > @@ -744,6 +745,11 @@ int main(int argc, char **argv, char **envp) > } > } > > + /* Resolve executable file name to full path name */ > + if (realpath(exec_path, real_exec_path)) { > + exec_path = real_exec_path; > + } > + > /* > * get binfmt_misc flags > * but only if not already done by parse_args() above > diff --git a/linux-user/syscall.c b/linux-user/syscall.c > index 0468a1bad7..71ae867024 100644 > --- a/linux-user/syscall.c > +++ b/linux-user/syscall.c > @@ -10011,18 +10011,11 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int num, abi_long arg1, > /* Short circuit this for the magic exe check. */ > ret = -TARGET_EINVAL; > } else if (is_proc_myself((const char *)p, "exe")) { > - char real[PATH_MAX], *temp; > - temp = realpath(exec_path, real); > - /* Return value is # of bytes that we wrote to the buffer. */ > - if (temp == NULL) { > - ret = get_errno(-1); > - } else { > - /* Don't worry about sign mismatch as earlier mapping > - * logic would have thrown a bad address error. */ > - ret = MIN(strlen(real), arg3); > - /* We cannot NUL terminate the string. */ > - memcpy(p2, real, ret); > - } > + /* Don't worry about sign mismatch as earlier mapping > + * logic would have thrown a bad address error. */ > + ret = MIN(strlen(exec_path), arg3); > + /* We cannot NUL terminate the string. */ > + memcpy(p2, exec_path, ret); > } else { > ret = get_errno(readlink(path(p), p2, arg3)); > } > @@ -10043,18 +10036,11 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int num, abi_long arg1, > /* Short circuit this for the magic exe check. */ > ret = -TARGET_EINVAL; > } else if (is_proc_myself((const char *)p, "exe")) { > - char real[PATH_MAX], *temp; > - temp = realpath(exec_path, real); > - /* Return value is # of bytes that we wrote to the buffer. */ > - if (temp == NULL) { > - ret = get_errno(-1); > - } else { > - /* Don't worry about sign mismatch as earlier mapping > - * logic would have thrown a bad address error. */ > - ret = MIN(strlen(real), arg4); > - /* We cannot NUL terminate the string. */ > - memcpy(p2, real, ret); > - } > + /* Don't worry about sign mismatch as earlier mapping > + * logic would have thrown a bad address error. */ > + ret = MIN(strlen(exec_path), arg4); > + /* We cannot NUL terminate the string. */ > + memcpy(p2, exec_path, ret); > } else { > ret = get_errno(readlinkat(arg1, path(p), p2, arg4)); > } > -- > 2.38.1 > > Reviewed-by: Laurent Vivier <laurent@vivier.eu>
© 2016 - 2024 Red Hat, Inc.