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