From: Earl Chew <echew@ixiacom.com>
Date: Wed, 21 Mar 2012 23:33:43 +0000 (-0700)
Subject: seq_file: fix mishandling of consecutive pread() invocations.
X-Git-Tag: v3.4-rc1~158^2~88
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=7904ac84244b59f536c2a5d1066a10f46df07b08;p=pandora-kernel.git

seq_file: fix mishandling of consecutive pread() invocations.

The following program illustrates the problem:

    char buf[8192];

    int fd = open("/proc/self/maps", O_RDONLY);

    n = pread(fd, buf, sizeof(buf), 0);
    printf("%d\n", n);

    /* lseek(fd, 0, SEEK_CUR); */ /* Uncomment to work around */

    n = pread(fd, buf, sizeof(buf), 0);
    printf("%d\n", n);

The second printf() prints zero, but uncommenting the lseek() corrects its
behaviour.

To fix, make seq_read() mirror seq_lseek() when processing changes in
*ppos.  Restore m->version first, then if required traverse and update
read_pos on success.

Addresses https://bugzilla.kernel.org/show_bug.cgi?id=11856

Signed-off-by: Earl Chew <echew@ixiacom.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

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