Re: [OE-core] [PATCH] pseudo: do not expand symlinks in /proc

["Randy MacLeod" <randy.macleod@windriver.com>]

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pseduo patches are usually sent to the yocto list so
I've added that list and only BCCed oe-core here so
people know where to look for follow-up.


On 2020-09-25 1:05 p.m., Sakib Sajal wrote:
> From: Matt Cowell <matt.cowell@nokia.com>
>
> 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:
> timed builds before and after applying patch, without significant
> measurable difference.
> $ bitbake -c compile <image>; time bitbake <image>
>
> installed pseudo on an image and was unable to reproduce the test
> on bug report after applying the patch.

There might be a better test so please let Sakib know if so.

Sakib,
   If there's a v2 or in future work, please give the actual results
such as:

   5 trials with an average time of 18m:14s and a range of 22 seconds
   on a build host that no one else was using.

This will help people to understand what you mean by
    "without significant measurable difference.

Thanks for testing and sending this change.

../Randy

>
> FIXES: Bug 13288
>
> Signed-off-by: Sakib Sajal <sakib.sajal@windriver.com>
> ---
>   pseudo_util.c | 27 +++++++++++++++++++++++++++
>   1 file changed, 27 insertions(+)
>
> diff --git a/pseudo_util.c b/pseudo_util.c
> index c867ed6..bce4d1e 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;
> @@ -677,6 +684,26 @@ 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;
>
> 
>

-- 
# Randy MacLeod
# Wind River Linux


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