From: Vasily Averin vvs@virtuozzo.com
commit 6c871b7314dde9ab64f20de8f5aa3d01be4518e8 upstream.
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"
/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: 1f4aace60b0e ("fs/seq_file.c: simplify seq_file iteration code ...") Link: https://bugzilla.kernel.org/show_bug.cgi?id=206283 Signed-off-by: Vasily 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: Kees Cook keescook@chromium.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/pstore/inode.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
--- a/fs/pstore/inode.c +++ b/fs/pstore/inode.c @@ -87,11 +87,11 @@ static void *pstore_ftrace_seq_next(stru 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 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",