| Message ID | 20220404210131.702898-1-adhemerval.zanella@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | [v3] linux: Fix __closefrom_fallback iterates until max int (BZ#28993) | expand |
* Adhemerval Zanella via Libc-alpha: > The __closefrom_fallback tries to get a available file descriptor > if the initial open ("/proc/self/fd/", ...) fails. It assumes the > failure would be only if procfs is not mount (ENOENT), however if > the the proc file is not accessible (due some other kernel filtering > such apparmor) it will iterate over a potentially large file set > issuing close calls. > > It should only try the close fallback if open returns EMFILE. The last line no longer matches the patch. Rest looks okay. Thanks, Florian
On 05/04/2022 04:09, Florian Weimer wrote: > * Adhemerval Zanella via Libc-alpha: > >> The __closefrom_fallback tries to get a available file descriptor >> if the initial open ("/proc/self/fd/", ...) fails. It assumes the >> failure would be only if procfs is not mount (ENOENT), however if >> the the proc file is not accessible (due some other kernel filtering >> such apparmor) it will iterate over a potentially large file set >> issuing close calls. >> >> It should only try the close fallback if open returns EMFILE. > > The last line no longer matches the patch. Ack, I will update it. > > Rest looks okay. Thanks.
diff --git a/sysdeps/unix/sysv/linux/closefrom_fallback.c b/sysdeps/unix/sysv/linux/closefrom_fallback.c index 60101aa3ba..a9dd0c46b2 100644 --- a/sysdeps/unix/sysv/linux/closefrom_fallback.c +++ b/sysdeps/unix/sysv/linux/closefrom_fallback.c @@ -30,16 +30,16 @@ _Bool __closefrom_fallback (int from, _Bool dirfd_fallback) { - bool ret = false; - int dirfd = __open_nocancel (FD_TO_FILENAME_PREFIX, O_RDONLY | O_DIRECTORY, 0); if (dirfd == -1) { - /* The closefrom should work even when process can't open new files. */ - if (errno == ENOENT || !dirfd_fallback) - goto err; + /* Return if procfs can not be opened for some reason. */ + if ((errno != EMFILE && errno != ENFILE && errno != ENOMEM) + || !dirfd_fallback) + return false; + /* The closefrom should work even when process can't open new files. */ for (int i = from; i < INT_MAX; i++) { int r = __close_nocancel (i); @@ -54,6 +54,7 @@ __closefrom_fallback (int from, _Bool dirfd_fallback) } char buffer[1024]; + bool ret = false; while (true) { ssize_t ret = __getdents64 (dirfd, buffer, sizeof (buffer));
The __closefrom_fallback tries to get a available file descriptor if the initial open ("/proc/self/fd/", ...) fails. It assumes the failure would be only if procfs is not mount (ENOENT), however if the the proc file is not accessible (due some other kernel filtering such apparmor) it will iterate over a potentially large file set issuing close calls. It should only try the close fallback if open returns EMFILE. Checked on x86_64-linux-gnu. --- sysdeps/unix/sysv/linux/closefrom_fallback.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-)