| Message ID | 20210419123630.62212-1-hello@oswalpalash.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | io_uring: check ctx->sq_data before io_sq_offload_start | expand |
On 4/19/21 6:36 AM, Palash Oswal wrote: > syzkaller identified KASAN: null-ptr-deref Read in io_uring_create > bug on the stable 5.11-y tree. > > BUG: KASAN: null-ptr-deref in io_sq_offload_start fs/io_uring.c:8254 [inline] > BUG: KASAN: null-ptr-deref in io_disable_sqo_submit fs/io_uring.c:8999 [inline] > BUG: KASAN: null-ptr-deref in io_uring_create+0x1275/0x22f0 fs/io_uring.c:9824 > Read of size 8 at addr 0000000000000068 by task syz-executor.0/4350 > > A simple reproducer for this bug is: > > int main(void) > { > syscall(__NR_mmap, 0x20000000ul, 0x1000000ul, 7ul, 0x32ul, -1, 0ul); > intptr_t res = 0; > pid_t parent = getpid(); > *(uint32_t*)0x20000084 = 0; > *(uint32_t*)0x20000088 = 0x42; > *(uint32_t*)0x2000008c = 0; > *(uint32_t*)0x20000090 = 0; > *(uint32_t*)0x20000098 = -1; > *(uint32_t*)0x2000009c = 0; > *(uint32_t*)0x200000a0 = 0; > *(uint32_t*)0x200000a4 = 0; > if (fork() == 0) { > kill(parent,SIGKILL); > exit(0); > } > res = syscall(__NR_io_uring_setup, 0x7994, 0x20000080ul); > return 0; > } > > Due to the SIGKILL sent to the process before io_uring_setup > completes, ctx->sq_data is NULL. Therefore, io_sq_offload_start > does a null pointer dereferenced read. More details on this bug > are in [1]. Discussion for this patch happened in [2]. > > [1] https://oswalpalash.com/exploring-null-ptr-deref-io-uring-submit > [2] https://lore.kernel.org/io-uring/a08121be-f481-e9f8-b28d-3eb5d4f > a5b76@gmail.com/ This should be a backport of the 5.12 fix, not a separate patch.
diff --git a/fs/io_uring.c b/fs/io_uring.c index 95b4a89dad4e..82a89ff315a4 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -8995,7 +8995,7 @@ static void io_disable_sqo_submit(struct io_ring_ctx *ctx) { mutex_lock(&ctx->uring_lock); ctx->sqo_dead = 1; - if (ctx->flags & IORING_SETUP_R_DISABLED) + if (ctx->flags & IORING_SETUP_R_DISABLED && ctx->sq_data) io_sq_offload_start(ctx); mutex_unlock(&ctx->uring_lock);
syzkaller identified KASAN: null-ptr-deref Read in io_uring_create bug on the stable 5.11-y tree. BUG: KASAN: null-ptr-deref in io_sq_offload_start fs/io_uring.c:8254 [inline] BUG: KASAN: null-ptr-deref in io_disable_sqo_submit fs/io_uring.c:8999 [inline] BUG: KASAN: null-ptr-deref in io_uring_create+0x1275/0x22f0 fs/io_uring.c:9824 Read of size 8 at addr 0000000000000068 by task syz-executor.0/4350 A simple reproducer for this bug is: int main(void) { syscall(__NR_mmap, 0x20000000ul, 0x1000000ul, 7ul, 0x32ul, -1, 0ul); intptr_t res = 0; pid_t parent = getpid(); *(uint32_t*)0x20000084 = 0; *(uint32_t*)0x20000088 = 0x42; *(uint32_t*)0x2000008c = 0; *(uint32_t*)0x20000090 = 0; *(uint32_t*)0x20000098 = -1; *(uint32_t*)0x2000009c = 0; *(uint32_t*)0x200000a0 = 0; *(uint32_t*)0x200000a4 = 0; if (fork() == 0) { kill(parent,SIGKILL); exit(0); } res = syscall(__NR_io_uring_setup, 0x7994, 0x20000080ul); return 0; } Due to the SIGKILL sent to the process before io_uring_setup completes, ctx->sq_data is NULL. Therefore, io_sq_offload_start does a null pointer dereferenced read. More details on this bug are in [1]. Discussion for this patch happened in [2]. [1] https://oswalpalash.com/exploring-null-ptr-deref-io-uring-submit [2] https://lore.kernel.org/io-uring/a08121be-f481-e9f8-b28d-3eb5d4f a5b76@gmail.com/ Signed-off-by: Palash Oswal <hello@oswalpalash.com> --- fs/io_uring.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) base-commit: 2aa8861eab092599ad566c5b20d7452d9ec0ca8e