On Mon, 2021-10-25 at 14:03 -0400, Sakib Sajal wrote:
> From: Matt Cowell <[email protected]>
>
> 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 <[email protected]>
> ---
> 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);
> + }
> + }
> +
Above this code, there is a call:
if (!pseudo_real_lstat || (pseudo_real_lstat(newpath, buf) == -1)) {
so we do have a statfs structure populated. Can we test buf.f_type ==
PROC_SUPER_MAGIC on that instead of calling open()? Or does that not contain the
right information?
Cheers,
Richard
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