diff options
authorVasily Averin <vvs@virtuozzo.com>2020-04-10 14:34:06 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-04-10 15:36:22 -0700
commit3bfa7e141b0bbb818b25e0daafb65aee92e49ac4 (patch)
parentcb8d9937e85559ea0ad1f4f83df8ad1288fed47d (diff)
fs/seq_file.c: seq_read(): add info message about buggy .next functions
Patch series "seq_file .next functions should increase position index". In Aug 2018 NeilBrown noticed commit 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code and interface") "Some ->next functions do not increment *pos when they return NULL... Note that such ->next functions are buggy and should be fixed. A simple demonstration is dd if=/proc/swaps bs=1000 skip=1 Choose any block size larger than the size of /proc/swaps. This will always show the whole last line of /proc/swaps" Described problem is still actual. If you make lseek into middle of last output line following read will output end of last line and whole last line once again. $ dd if=/proc/swaps bs=1 # usual output Filename Type Size Used Priority /dev/dm-0 partition 4194812 97536 -2 104+0 records in 104+0 records out 104 bytes copied $ dd if=/proc/swaps bs=40 skip=1 # last line was generated twice dd: /proc/swaps: cannot skip to specified offset v/dm-0 partition 4194812 97536 -2 /dev/dm-0 partition 4194812 97536 -2 3+1 records in 3+1 records out 131 bytes copied There are lot of other affected files, I've found 30+ including /proc/net/ip_tables_matches and /proc/sysvipc/* I've sent patches into maillists of affected subsystems already, this patch-set fixes the problem in files related to pstore, tracing, gcov, sysvipc and other subsystems processed via linux-kernel@ mailing list directly https://bugzilla.kernel.org/show_bug.cgi?id=206283 This patch (of 4): Add debug code to seq_read() to detect missed or out-of-tree incorrect .next seq_file functions. [akpm@linux-foundation.org: s/pr_info/pr_info_ratelimited/, per Qian Cai] https://bugzilla.kernel.org/show_bug.cgi?id=206283 Signed-off-by: Vasily Averin <vvs@virtuozzo.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Cc: NeilBrown <neilb@suse.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Ingo Molnar <mingo@redhat.com> Cc: Manfred Spraul <manfred@colorfullife.com> Cc: Peter Oberparleiter <oberpar@linux.ibm.com> Cc: Waiman Long <longman@redhat.com> Link: http://lkml.kernel.org/r/244674e5-760c-86bd-d08a-047042881748@virtuozzo.com Link: http://lkml.kernel.org/r/7c24087c-e280-e580-5b0c-0cdaeb14cd18@virtuozzo.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 files changed, 5 insertions, 2 deletions
diff --git a/fs/seq_file.c b/fs/seq_file.c
index 79781ebd2145..70f5fdf99bf6 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -232,9 +232,12 @@ Fill:
loff_t pos = m->index;
p = m->op->next(m, p, &m->index);
- if (pos == m->index)
- /* Buggy ->next function */
+ if (pos == m->index) {
+ pr_info_ratelimited("buggy seq_file .next function %ps "
+ "did not updated position index\n",
+ m->op->next);
+ }
if (!p || IS_ERR(p)) {
err = PTR_ERR(p);