This is a note to let you know that I've just added the patch titled
seq_file: always update file->f_pos in seq_lseek()
to the 3.11-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
seq_file-always-update-file-f_pos-in-seq_lseek.patch
and it can be found in the queue-3.11 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From 05e16745c0c471bba313961b605b6da3b21a853d Mon Sep 17 00:00:00 2001
From: Gu Zheng <[email protected]>
Date: Fri, 25 Oct 2013 18:15:06 +0800
Subject: seq_file: always update file->f_pos in seq_lseek()
From: Gu Zheng <[email protected]>
commit 05e16745c0c471bba313961b605b6da3b21a853d upstream.
This issue was first pointed out by Jiaxing Wang several months ago, but no
further comments:
https://lkml.org/lkml/2013/6/29/41
As we know pread() does not change f_pos, so after pread(), file->f_pos
and m->read_pos become different. And seq_lseek() does not update file->f_pos
if offset equals to m->read_pos, so after pread() and seq_lseek()(lseek to
m->read_pos), then a subsequent read may read from a wrong position, the
following program produces the problem:
char str1[32] = { 0 };
char str2[32] = { 0 };
int poffset = 10;
int count = 20;
/*open any seq file*/
int fd = open("/proc/modules", O_RDONLY);
pread(fd, str1, count, poffset);
printf("pread:%s\n", str1);
/*seek to where m->read_pos is*/
lseek(fd, poffset+count, SEEK_SET);
/*supposed to read from poffset+count, but this read from position 0*/
read(fd, str2, count);
printf("read:%s\n", str2);
out put:
pread:
ck_netbios_ns 12665
read:
nf_conntrack_netbios
/proc/modules:
nf_conntrack_netbios_ns 12665 0 - Live 0xffffffffa038b000
nf_conntrack_broadcast 12589 1 nf_conntrack_netbios_ns, Live 0xffffffffa0386000
So we always update file->f_pos to offset in seq_lseek() to fix this issue.
Signed-off-by: Jiaxing Wang <[email protected]>
Signed-off-by: Gu Zheng <[email protected]>
Signed-off-by: Al Viro <[email protected]>
Cc: Jonghwan Choi <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
fs/seq_file.c | 2 ++
1 file changed, 2 insertions(+)
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -328,6 +328,8 @@ loff_t seq_lseek(struct file *file, loff
m->read_pos = offset;
retval = file->f_pos = offset;
}
+ } else {
+ file->f_pos = offset;
}
}
file->f_version = m->version;
Patches currently in stable-queue which might be from [email protected]
are
queue-3.11/seq_file-always-update-file-f_pos-in-seq_lseek.patch
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