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    Subject[PATCH 5.4 42/60] keys: Fix proc_keys_next to increase position index
    Date
    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
    @@ -139,6 +139,8 @@ 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;
    }


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