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authorNeilBrown <neilb@suse.com>2019-08-13 15:37:44 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2019-08-13 16:06:52 -0700
commit6a2aeab59e97101b4001bac84388fc49a992f87e (patch)
treef2a3b5188de3354b5f53d1b605270407d6b6fb82
parentec9f02384f6053f2a5417e82b65078edc5364a8d (diff)
download96b-common-6a2aeab59e97101b4001bac84388fc49a992f87e.tar.gz
seq_file: fix problem when seeking mid-record
If you use lseek or similar (e.g. pread) to access a location in a seq_file file that is within a record, rather than at a record boundary, then the first read will return the remainder of the record, and the second read will return the whole of that same record (instead of the next record). When seeking to a record boundary, the next record is correctly returned. This bug was introduced by a recent patch (identified below). Before that patch, seq_read() would increment m->index when the last of the buffer was returned (m->count == 0). After that patch, we rely on ->next to increment m->index after filling the buffer - but there was one place where that didn't happen. Link: https://lkml.kernel.org/lkml/877e7xl029.fsf@notabene.neil.brown.name/ Fixes: 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code and interface") Signed-off-by: NeilBrown <neilb@suse.com> Reported-by: Sergei Turchanov <turchanov@farpost.com> Tested-by: Sergei Turchanov <turchanov@farpost.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Markus Elfring <Markus.Elfring@web.de> Cc: <stable@vger.kernel.org> [4.19+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/seq_file.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/seq_file.c b/fs/seq_file.c
index 04f09689cd6d..1600034a929b 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -119,6 +119,7 @@ static int traverse(struct seq_file *m, loff_t offset)
}
if (seq_has_overflowed(m))
goto Eoverflow;
+ p = m->op->next(m, p, &m->index);
if (pos + m->count > offset) {
m->from = offset - pos;
m->count -= m->from;
@@ -126,7 +127,6 @@ static int traverse(struct seq_file *m, loff_t offset)
}
pos += m->count;
m->count = 0;
- p = m->op->next(m, p, &m->index);
if (pos == offset)
break;
}