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libapparmor: add a workaround for procfs returning a bad stat.st_size value

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For some longer pathname fstat is returning a bad size resulting in
the path being truncated. Fix this by detecting a potential truncation
and re-doing the readlink.

Signed-off-by: John Johansen <john.johansen@canonical.com>
Acked-by: Christian Boltz <apparmor@cboltz.de>
This commit is contained in:
John Johansen 2018-03-08 23:15:12 -08:00
parent 1328a42d5a
commit 4814763c97
1 changed files with 10 additions and 4 deletions
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14
libraries/libapparmor/src/policy_cache.c
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@ -102,7 +102,7 @@ static char *path_from_fd(int fd)
autoclose int proc_fd = -1;
struct stat proc_stat;
char *path;
ssize_t path_len;
ssize_t size, path_len;
if (asprintf(&proc_path, "/proc/self/fd/%d", fd) == -1) {
proc_path = NULL;
@ -122,7 +122,9 @@ static char *path_from_fd(int fd)
return NULL;
}
path = malloc(proc_stat.st_size + 1);
size = proc_stat.st_size;
repeat:
path = malloc(size + 1);
if (!path)
return NULL;
@ -131,10 +133,14 @@ static char *path_from_fd(int fd)
* (O_PATH | O_NOFOLLOW) can be used as the dirfd with an empty string
* as the path. readlinkat() will operate on the symlink inode.
*/
path_len = readlinkat(proc_fd, "", path, proc_stat.st_size);
path_len = readlinkat(proc_fd, "", path, size);
if (path_len == -1)
return NULL;
if (path_len == size) {
free(path);
size = size * 2;
goto repeat;
}
path[path_len] = '\0';
return path;
}