From: Vasily Averin vvs@virtuozzo.com
commit 86d32f9a7c54ad74f4514d7fef7c847883207291 upstream.
If seq_file .next function does not change position index, read after some lseek can generate unexpected output:
$ dd if=/proc/keys bs=1 # full usual output 0f6bfdf5 I--Q--- 2 perm 3f010000 1000 1000 user 4af2f79ab8848d0a: 740 1fb91b32 I--Q--- 3 perm 1f3f0000 1000 65534 keyring _uid.1000: 2 27589480 I--Q--- 1 perm 0b0b0000 0 0 user invocation_id: 16 2f33ab67 I--Q--- 152 perm 3f030000 0 0 keyring _ses: 2 33f1d8fa I--Q--- 4 perm 3f030000 1000 1000 keyring _ses: 1 3d427fda I--Q--- 2 perm 3f010000 1000 1000 user 69ec44aec7678e5a: 740 3ead4096 I--Q--- 1 perm 1f3f0000 1000 65534 keyring _uid_ses.1000: 1 521+0 records in 521+0 records out 521 bytes copied, 0,00123769 s, 421 kB/s
But a read after lseek in middle of last line results in the partial last line and then a repeat of the final line:
$ dd if=/proc/keys bs=500 skip=1 dd: /proc/keys: cannot skip to specified offset g _uid_ses.1000: 1 3ead4096 I--Q--- 1 perm 1f3f0000 1000 65534 keyring _uid_ses.1000: 1 0+1 records in 0+1 records out 97 bytes copied, 0,000135035 s, 718 kB/s
and a read after lseek beyond end of file results in the last line being shown:
$ dd if=/proc/keys bs=1000 skip=1 # read after lseek beyond end of file dd: /proc/keys: cannot skip to specified offset 3ead4096 I--Q--- 1 perm 1f3f0000 1000 65534 keyring _uid_ses.1000: 1 0+1 records in 0+1 records out 76 bytes copied, 0,000119981 s, 633 kB/s
See https://bugzilla.kernel.org/show_bug.cgi?id=206283
Fixes: 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code ...") Signed-off-by: Vasily Averin vvs@virtuozzo.com Signed-off-by: David Howells dhowells@redhat.com Reviewed-by: Jarkko Sakkinen jarkko.sakkinen@linux.intel.com Cc: stable@vger.kernel.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- security/keys/proc.c | 2 ++ 1 file changed, 2 insertions(+)
--- a/security/keys/proc.c +++ b/security/keys/proc.c @@ -144,6 +144,8 @@ static void *proc_keys_next(struct seq_f n = key_serial_next(p, v); if (n) *_pos = key_node_serial(n); + else + (*_pos)++; return n; }