Messages in this thread Patch in this message | | | From | David Howells <> | Subject | Re: [syzbot] KASAN: null-ptr-deref Read in __free_pages | Date | Mon, 21 Mar 2022 08:46:51 +0000 |
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Hi Fabio,
How about using my patch instead? I wonder if __free_pages() should check for a NULL pages pointer...
David --- watch_queue: Fix NULL dereference in error cleanup
In watch_queue_set_size(), the error cleanup code doesn't take account of the fact that __free_page() can't handle a NULL pointer when trying to free up buffer pages that did get allocated.
Fix this by only calling __free_page() on non-NULL pointers extracted from the list (the list was allocated by kcalloc() so was pre-cleared).
Without the fix, this can lead to something like the following:
BUG: KASAN: null-ptr-deref in __free_pages+0x1f/0x1b0 mm/page_alloc.c:5473 Read of size 4 at addr 0000000000000034 by task syz-executor168/3599 ... Call Trace: <TASK> __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106 __kasan_report mm/kasan/report.c:446 [inline] kasan_report.cold+0x66/0xdf mm/kasan/report.c:459 check_region_inline mm/kasan/generic.c:183 [inline] kasan_check_range+0x13d/0x180 mm/kasan/generic.c:189 instrument_atomic_read include/linux/instrumented.h:71 [inline] atomic_read include/linux/atomic/atomic-instrumented.h:27 [inline] page_ref_count include/linux/page_ref.h:67 [inline] put_page_testzero include/linux/mm.h:717 [inline] __free_pages+0x1f/0x1b0 mm/page_alloc.c:5473 watch_queue_set_size+0x499/0x630 kernel/watch_queue.c:275 pipe_ioctl+0xac/0x2b0 fs/pipe.c:632 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:874 [inline] __se_sys_ioctl fs/ioctl.c:860 [inline] __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:860 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x44/0xae
Fixes: c73be61cede5 ("pipe: Add general notification queue support") Reported-and-tested-by: syzbot+d55757faa9b80590767b@syzkaller.appspotmail.com Signed-off-by: David Howells <dhowells@redhat.com> --- kernel/watch_queue.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c index 00703444a219..09f35bab496e 100644 --- a/kernel/watch_queue.c +++ b/kernel/watch_queue.c @@ -272,7 +272,8 @@ long watch_queue_set_size(struct pipe_inode_info *pipe, unsigned int nr_notes) error_p: for (i = 0; i < nr_pages; i++) - __free_page(pages[i]); + if (pages[i]) + __free_page(pages[i]); kfree(pages); error: (void) account_pipe_buffers(pipe->user, nr_pages, pipe->nr_accounted);
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