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| author | Matthew Wilcox (Oracle) <willy@infradead.org> | 2022-03-28 19:25:11 -0400 |
|---|---|---|
| committer | Matthew Wilcox (Oracle) <willy@infradead.org> | 2022-03-28 19:25:11 -0400 |
| commit | 3e3c658055c002900982513e289398a1aad4a488 (patch) | |
| tree | 53911e5e6154d643cfc9eb5cd7f375470ea61831 /lib | |
| parent | 22f56b8e890d4e2835951b437bb6eeebfd1cb18b (diff) | |
| download | linux-3e3c658055c002900982513e289398a1aad4a488.tar.bz2 | |
XArray: Fix xas_create_range() when multi-order entry present
If there is already an entry present that is of order >= XA_CHUNK_SHIFT
when we call xas_create_range(), xas_create_range() will misinterpret
that entry as a node and dereference xa_node->parent, generally leading
to a crash that looks something like this:
general protection fault, probably for non-canonical address 0xdffffc0000000001:
0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
CPU: 0 PID: 32 Comm: khugepaged Not tainted 5.17.0-rc8-syzkaller-00003-g56e337f2cf13 #0
RIP: 0010:xa_parent_locked include/linux/xarray.h:1207 [inline]
RIP: 0010:xas_create_range+0x2d9/0x6e0 lib/xarray.c:725
It's deterministically reproducable once you know what the problem is,
but producing it in a live kernel requires khugepaged to hit a race.
While the problem has been present since xas_create_range() was
introduced, I'm not aware of a way to hit it before the page cache was
converted to use multi-index entries.
Fixes: 6b24ca4a1a8d ("mm: Use multi-index entries in the page cache")
Reported-by: syzbot+0d2b0bf32ca5cfd09f2e@syzkaller.appspotmail.com
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/test_xarray.c | 22 | ||||
| -rw-r--r-- | lib/xarray.c | 2 |
2 files changed, 24 insertions, 0 deletions
diff --git a/lib/test_xarray.c b/lib/test_xarray.c index 8b1c318189ce..e77d4856442c 100644 --- a/lib/test_xarray.c +++ b/lib/test_xarray.c @@ -1463,6 +1463,25 @@ unlock: XA_BUG_ON(xa, !xa_empty(xa)); } +static noinline void check_create_range_5(struct xarray *xa, + unsigned long index, unsigned int order) +{ + XA_STATE_ORDER(xas, xa, index, order); + unsigned int i; + + xa_store_order(xa, index, order, xa_mk_index(index), GFP_KERNEL); + + for (i = 0; i < order + 10; i++) { + do { + xas_lock(&xas); + xas_create_range(&xas); + xas_unlock(&xas); + } while (xas_nomem(&xas, GFP_KERNEL)); + } + + xa_destroy(xa); +} + static noinline void check_create_range(struct xarray *xa) { unsigned int order; @@ -1490,6 +1509,9 @@ static noinline void check_create_range(struct xarray *xa) check_create_range_4(xa, (3U << order) + 1, order); check_create_range_4(xa, (3U << order) - 1, order); check_create_range_4(xa, (1U << 24) + 1, order); + + check_create_range_5(xa, 0, order); + check_create_range_5(xa, (1U << order), order); } check_create_range_3(); diff --git a/lib/xarray.c b/lib/xarray.c index 6f47f6375808..757644617b9b 100644 --- a/lib/xarray.c +++ b/lib/xarray.c @@ -722,6 +722,8 @@ void xas_create_range(struct xa_state *xas) for (;;) { struct xa_node *node = xas->xa_node; + if (node->shift >= shift) + break; xas->xa_node = xa_parent_locked(xas->xa, node); xas->xa_offset = node->offset - 1; if (node->offset != 0) |