diff options
author | Gu Zheng <guz.fnst@cn.fujitsu.com> | 2013-10-25 18:15:06 +0800 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2013-11-13 12:05:34 +0900 |
commit | dad483b78d280665a110591fd418535e0f9791dc (patch) | |
tree | 939d5b7651c4260bf8665b39986a056b8dd41a16 | |
parent | 2233b4db914786e69960d717a3019c87ba3bb5a5 (diff) | |
download | linux-stable-dad483b78d280665a110591fd418535e0f9791dc.tar.gz linux-stable-dad483b78d280665a110591fd418535e0f9791dc.tar.bz2 linux-stable-dad483b78d280665a110591fd418535e0f9791dc.zip |
seq_file: always update file->f_pos in seq_lseek()
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 <hello.wjx@gmail.com>
Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jonghwan Choi <jhbird.choi@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r-- | fs/seq_file.c | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/fs/seq_file.c b/fs/seq_file.c index 774c1eb7f1c9..3dd44db1465e 100644 --- a/fs/seq_file.c +++ b/fs/seq_file.c @@ -328,6 +328,8 @@ loff_t seq_lseek(struct file *file, loff_t offset, int whence) m->read_pos = offset; retval = file->f_pos = offset; } + } else { + file->f_pos = offset; } } file->f_version = m->version; |