From: Vasily Averin <[email protected]>
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
$ dd if=/proc/keys bs=500 skip=1 # read after lseek in middle of last line
dd: /proc/keys: cannot skip to specified offset
g _uid_ses.1000: 1 <<<< end of last line
3ead4096 I--Q--- 1 perm 1f3f0000 1000 65534 keyring _uid_ses.1000: 1
<<<< and whole last line again
0+1 records in
0+1 records out
97 bytes copied, 0,000135035 s, 718 kB/s
$ 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
<<<< generates last line
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
Cc: [email protected]
Fixes: 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code ...")
Signed-off-by: Vasily Averin <[email protected]>
Signed-off-by: David Howells <[email protected]>
---
security/keys/proc.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/security/keys/proc.c b/security/keys/proc.c
index 415f3f1c2da0..d0cde6685627 100644
--- a/security/keys/proc.c
+++ b/security/keys/proc.c
@@ -139,6 +139,8 @@ static void *proc_keys_next(struct seq_file *p, void *v, loff_t *_pos)
n = key_serial_next(p, v);
if (n)
*_pos = key_node_serial(n);
+ else
+ (*_pos)++;
return n;
}
On Tue, Apr 14, 2020 at 09:33:16PM +0100, David Howells wrote:
> From: Vasily Averin <[email protected]>
>
> 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
>
> $ dd if=/proc/keys bs=500 skip=1 # read after lseek in middle of last line
> dd: /proc/keys: cannot skip to specified offset
> g _uid_ses.1000: 1 <<<< end of last line
> 3ead4096 I--Q--- 1 perm 1f3f0000 1000 65534 keyring _uid_ses.1000: 1
> <<<< and whole last line again
> 0+1 records in
> 0+1 records out
> 97 bytes copied, 0,000135035 s, 718 kB/s
>
> $ 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
> <<<< generates last line
> 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
>
> Cc: [email protected]
# 4.19.x
> Fixes: 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code ...")
> Signed-off-by: Vasily Averin <[email protected]>
> Signed-off-by: David Howells <[email protected]>
Reviewed-by: Jarkko Sakkinen <[email protected]>
/Jarkko