[v2] xdp: remove WARN() from __xdp_reg_mem_model()

Commit Message

Daniil Dulov June 24, 2024, 8:07 a.m. UTC

Syzkaller reports a warning in __xdp_reg_mem_model().

The warning occurs only if __mem_id_init_hash_table() returns
an error. It returns the error in two cases:

  1. memory allocation fails;
  2. rhashtable_init() fails when some fields of rhashtable_params
     struct are not initialized properly.

The second case cannot happen since there is a static const
rhashtable_params struct with valid fields. So, warning is only triggered
when there is a problem with memory allocation.

Thus, there is no sense in using WARN() to handle this error and it can be
safely removed.

WARNING: CPU: 0 PID: 5065 at net/core/xdp.c:299 __xdp_reg_mem_model+0x2d9/0x650 net/core/xdp.c:299

CPU: 0 PID: 5065 Comm: syz-executor883 Not tainted 6.8.0-syzkaller-05271-gf99c5f563c17 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
RIP: 0010:__xdp_reg_mem_model+0x2d9/0x650 net/core/xdp.c:299

Call Trace:
 xdp_reg_mem_model+0x22/0x40 net/core/xdp.c:344
 xdp_test_run_setup net/bpf/test_run.c:188 [inline]
 bpf_test_run_xdp_live+0x365/0x1e90 net/bpf/test_run.c:377
 bpf_prog_test_run_xdp+0x813/0x11b0 net/bpf/test_run.c:1267
 bpf_prog_test_run+0x33a/0x3b0 kernel/bpf/syscall.c:4240
 __sys_bpf+0x48d/0x810 kernel/bpf/syscall.c:5649
 __do_sys_bpf kernel/bpf/syscall.c:5738 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:5736 [inline]
 __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5736
 do_syscall_64+0xfb/0x240
 entry_SYSCALL_64_after_hwframe+0x6d/0x75

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

Fixes: 8d5d88527587 ("xdp: rhashtable with allocator ID to pointer mapping")
Signed-off-by: Daniil Dulov <[e-mail]>
Acked-by: Jesper Dangaard Brouer <[e-mail]>
---
v2: Removed unnecessary brackets as Jakub Kicinski <[e-mail]>
suggested, also added Acked-by Jesper Dangaard Brouer <[e-mail]>
Link: https://lore.kernel.org/all/[e-mail]/

 net/core/xdp.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

Comments

[e-mail] June 24, 2024, 10:10 a.m. UTC | #1

Hello:

This patch was applied to bpf/bpf.git (master)
by Daniel Borkmann <[e-mail]>:

On Mon, 24 Jun 2024 11:07:47 +0300 you wrote:
> Syzkaller reports a warning in __xdp_reg_mem_model().
> 
> The warning occurs only if __mem_id_init_hash_table() returns
> an error. It returns the error in two cases:
> 
>   1. memory allocation fails;
>   2. rhashtable_init() fails when some fields of rhashtable_params
>      struct are not initialized properly.
> 
> [...]

Here is the summary with links:
  - [v2] xdp: remove WARN() from __xdp_reg_mem_model()
    https://git.kernel.org/bpf/bpf/c/de081f82e810

You are awesome, thank you!

Patch

diff --git a/net/core/xdp.c b/net/core/xdp.c
index 41693154e426..022c12059cf2 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -295,10 +295,8 @@  static struct xdp_mem_allocator *__xdp_reg_mem_model(struct xdp_mem_info *mem,
 		mutex_lock(&mem_id_lock);
 		ret = __mem_id_init_hash_table();
 		mutex_unlock(&mem_id_lock);
-		if (ret < 0) {
-			WARN_ON(1);
+		if (ret < 0)
 			return ERR_PTR(ret);
-		}
 	}
 
 	xdp_alloc = kzalloc(sizeof(*xdp_alloc), gfp);