commit 86d32f9a7c 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: 1f4aace60b ("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>
a0aaafe7ce