[pseudo] pseudo_fix_path: do not expand symlinks in /proc
From: Sakib Sajal <hidden>
Date: 2021-10-25 18:03:17
Subsystem:
the rest · Maintainer:
Linus Torvalds
From: Matt Cowell <redacted>
Some symlinks in /proc, such as those under /proc/[pid]/fd,
/proc/[pid]/cwd, and /proc/[pid]/exe that are not real and should not
have readlink called on them. These look like symlinks, but behave like
hardlinks. Readlink does not return actual paths. Previously
pseudo_fix_path would expand files such as /dev/stdin to paths such as
/proc/6680/fd/pipe:[1270830076] which do not exist.
This issue affects:
- deleted files
- deleted directories
- fifos
- sockets
- anon_inodes (epoll, eventfd, inotify, signalfd, timerfd, etc)
Testing:
- run_tests: all tests passed. Checked the test output to make
sure the new codepath gets executed.
- perftest: measured time before and after applying the patch
had insignificant differences (roughly ~1%)
- world build: completed without warning/errors
Signed-off-by: Sakib Sajal <redacted>
---
pseudo_util.c | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)
diff --git a/pseudo_util.c b/pseudo_util.c
index b6980c2..b35a34e 100644
--- a/pseudo_util.c
+++ b/pseudo_util.c@@ -21,6 +21,8 @@ #include <sys/time.h> #include <unistd.h> #include <limits.h> +#include <sys/vfs.h> +#include <linux/magic.h> /* see the comments below about (*real_regcomp)() */ #include <dlfcn.h>
@@ -29,6 +31,11 @@ #include "pseudo_ipc.h" #include "pseudo_db.h" +/* O_PATH is defined in glibc 2.16 and later only */ +#ifndef O_PATH +#define O_PATH 010000000 +#endif + struct pseudo_variables { char *key; size_t key_len;
@@ -678,6 +685,26 @@ pseudo_append_element(char *newpath, char *root, size_t allocated, char **pcurre */ if (!leave_this && is_dir) { int is_link = S_ISLNK(buf->st_mode); + + /* do not expand symlinks in the proc filesystem, since they may not be real */ + if (is_link) { + struct statfs sfs; + int fd; + + /* statfs follows symlinks, so use fstatfs */ + fd = open(newpath, O_CLOEXEC | O_PATH | O_NOFOLLOW); + if (-1 != fd) { + if (0 == fstatfs(fd, &sfs) && sfs.f_type == PROC_SUPER_MAGIC) { + pseudo_debug(PDBGF_PATH | PDBGF_VERBOSE, + "pae: '%s' is procfs symlink, not expanding\n", + newpath); + is_link = 0; + } + + close(fd); + } + } + if (link_recursion >= PSEUDO_MAX_LINK_RECURSION && is_link) { pseudo_diag("link recursion too deep, not expanding path '%s'.\n", newpath); is_link = 0;
--
2.25.1