From 258bec39f3e58fcdb006028e5c5a1801136ef04a Mon Sep 17 00:00:00 2001 From: Helge Deller Date: Mon, 5 Dec 2022 12:38:25 +0100 Subject: [PATCH] linux-user: Fix access to /proc/self/exe 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 Reviewed-by: Laurent Vivier Message-Id: <20221205113825.20615-1-deller@gmx.de> Signed-off-by: Laurent Vivier --- linux-user/main.c | 6 ++++++ linux-user/syscall.c | 38 ++++++++++++++------------------------ 2 files changed, 20 insertions(+), 24 deletions(-) diff --git a/linux-user/main.c b/linux-user/main.c index 4ff30ff980..798fdc0bce 100644 --- a/linux-user/main.c +++ b/linux-user/main.c @@ -65,6 +65,7 @@ #endif char *exec_path; +char real_exec_path[PATH_MAX]; int singlestep; static const char *argv0; @@ -739,6 +740,11 @@ 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 */ diff --git a/linux-user/syscall.c b/linux-user/syscall.c index a6c426d73c..cc650d4ccb 100644 --- a/linux-user/syscall.c +++ b/linux-user/syscall.c @@ -9989,18 +9989,13 @@ 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)); } @@ -10021,18 +10016,13 @@ 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)); }