Commit 6c871b73 authored by Vasily Averin's avatar Vasily Averin Committed by Kees Cook

pstore: pstore_ftrace_seq_next should increase position index

In Aug 2018 NeilBrown noticed
commit 1f4aace6 ("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"

/proc/swaps output was fixed recently, however there are lot of other
affected files, and one of them is related to pstore subsystem.

If .next function does not change position index, following .show function
will repeat output related to current position index.

There are at least 2 related problems:
- read after lseek beyond end of file, described above by NeilBrown
  "dd if=<AFFECTED_FILE> bs=1000 skip=1" will generate whole last list
- read after lseek on in middle of last line will output expected rest of
  last line but then repeat whole last line once again.

If .show() function generates multy-line output (like
pstore_ftrace_seq_show() does ?) following bash script cycles endlessly

 $ q=;while read -r r;do echo "$((++q)) $r";done < AFFECTED_FILE

Unfortunately I'm not familiar enough to pstore subsystem and was unable
to find affected pstore-related file on my test node.

If .next function does not change position index, following .show function
will repeat output related to current position index.

Cc: stable@vger.kernel.org
Fixes: 1f4aace6 ("fs/seq_file.c: simplify seq_file iteration code ...")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=206283Signed-off-by: default avatarVasily Averin <vvs@virtuozzo.com>
Link: https://lore.kernel.org/r/4e49830d-4c88-0171-ee24-1ee540028dad@virtuozzo.com
[kees: with robustness tweak from Joel Fernandes <joelaf@google.com>]
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
parent e030b80f
......@@ -87,11 +87,11 @@ static void *pstore_ftrace_seq_next(struct seq_file *s, void *v, loff_t *pos)
struct pstore_private *ps = s->private;
struct pstore_ftrace_seq_data *data = v;
(*pos)++;
data->off += REC_SIZE;
if (data->off + REC_SIZE > ps->total_size)
return NULL;
(*pos)++;
return data;
}
......@@ -101,6 +101,9 @@ static int pstore_ftrace_seq_show(struct seq_file *s, void *v)
struct pstore_ftrace_seq_data *data = v;
struct pstore_ftrace_record *rec;
if (!data)
return 0;
rec = (struct pstore_ftrace_record *)(ps->record->buf + data->off);
seq_printf(s, "CPU:%d ts:%llu %08lx %08lx %ps <- %pS\n",
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment