On 9/19/26 02:42, Jiakai Xu wrote:

Commit 44e9eb5a7621 ("dma-buf/udmabuf: Disable the size limit by default") raised the default size_limit_mb from 64 to INT_MAX. With 4K pages, creating a buffer of more than INT_MAX / 8 pages (about 1 TB of pinned memory) now makes the two per-page pointer arrays in init_udmabuf() exceed what kvmalloc() can handle: kvmalloc() warns and fails when the requested size exceeds INT_MAX bytes (WARN_ON_ONCE in __kvmalloc_node_noprof), which is trivially triggerable from unprivileged users through the UDMABUF_CREATE ioctls:

WARNING: CPU: 0 PID: 412 at mm/slub.c:7021 __kvmalloc_node_noprof Call Trace: udmabuf_create udmabuf_ioctl_create_list

Restore a reasonable default limit of 256 MB, which is the value proposed in the RFC discussion that led to commit 44e9eb5a7621

That is way to low, we want to allocate multiple gigabytes using that API.

Please make that (((INT_MAX / sizeof(struct folio *)) - 1) >> 20) << PAGE_SHIFT.

That should allow to allocate a bit below 1TiB again without triggering the issue.

Regards, Christian.

("dma-buf/udmabuf: Disable the size limit by default") and comfortably covers the 8K video use cases cited there, while keeping the kvmalloc() request far below its threshold. The limit remains runtime-tunable via the size_limit_mb module parameter for setups that need more.

Fixes: 44e9eb5a7621 ("dma-buf/udmabuf: Disable the size limit by default") Assisted-by: OpenCode:DeepSeek-V4-Flash Signed-off-by: Jiakai Xu xujiakai24@mails.ucas.ac.cn

---

V1 -> V2:

• Instead of adding a pgcnt check in udmabuf_create(), restore a reasonable default size limit (256 MB), as suggested by Christian König.
• Drop the second Fixes tag; the regression is solely due to 44e9eb5a7621.
• Drop the "Cc: stable" tag; 44e9eb5a7621 is only in v7.3-rc1 and has not shipped in any released kernel yet.

V1: https://lore.kernel.org/all/20260918013434.1849135-1-xujiakai24@mails.ucas.a...

drivers/dma-buf/udmabuf.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c index df6dd00462423..4d90c2cb14225 100644 --- a/drivers/dma-buf/udmabuf.c +++ b/drivers/dma-buf/udmabuf.c @@ -20,9 +20,9 @@ static int list_limit = 1024; module_param(list_limit, int, 0644); MODULE_PARM_DESC(list_limit, "udmabuf_create_list->count limit. Default is 1024.");

-static int size_limit_mb = INT_MAX; +static int size_limit_mb = 256; module_param(size_limit_mb, int, 0644); -MODULE_PARM_DESC(size_limit_mb, "Max size of a dmabuf, in megabytes. Default is INT_MAX."); +MODULE_PARM_DESC(size_limit_mb, "Max size of a dmabuf, in megabytes. Default is 256.");

struct udmabuf { pgoff_t pagecount; -- 2.34.1

-- Below is the crash report: ------------[ cut here ]------------ WARNING: mm/slub.c:7013 at __kvmalloc_node_noprof+0x516/0x5d0 home/zzzrrll/tmp/kf_src/linux-7.3-rc2/mm/slub.c:7013, CPU#0: syz.5.27938/167363 Modules linked in: CPU: 0 UID: 0 PID: 167363 Comm: syz.5.27938 Tainted: G W L 7.3.0-rc2 #1 PREEMPT(full) Tainted: [W]=WARN, [L]=SOFTLOCKUP Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014 RIP: 0010:__kvmalloc_node_noprof+0x516/0x5d0 home/zzzrrll/tmp/kf_src/linux-7.3-rc2/mm/slub.c:7013 Code: 05 bf fa 2d 08 49 8b 0f c6 04 08 00 65 48 ff 0d 90 fa 2d 08 0f 85 4c fd ff ff e8 05 43 8c ff e9 42 fd ff ff e8 9b 86 0e 04 90 <0f> 0b 90 31 db e9 d2 fe ff ff f3 0f 1e fa 65 8b 05 8d fa 2d 08 89 RSP: 0018:ffffc90002bc3cf8 EFLAGS: 00010246 RAX: 0000000000000100 RBX: 0000000000000000 RCX: 0000008000000000 RDX: 0000008000000000 RSI: 0000000000000000 RDI: ffffffff835e3226 RBP: 00000000ffffffff R08: 00000000000028c0 R09: 00000000ffffffff R10: 0000000000000006 R11: 0000000000000002 R12: 0000008000000000 R13: 00000000000028c0 R14: 0000001000000000 R15: 0000008000000000 FS: 00007fc89ae45640(0000) GS:ffff8880f3de4000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000000110c2ff305 CR3: 000000002b3d4000 CR4: 0000000000752ef0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000006000 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 PKRU: 80000000 Call Trace:

<TASK> init_udmabuf home/zzzrrll/tmp/kf_src/linux-7.3-rc2/drivers/dma-buf/udmabuf.c:193 [inline] udmabuf_create+0x1b6/0x750 home/zzzrrll/tmp/kf_src/linux-7.3-rc2/drivers/dma-buf/udmabuf.c:386 udmabuf_ioctl_create home/zzzrrll/tmp/kf_src/linux-7.3-rc2/drivers/dma-buf/udmabuf.c:465 [inline] udmabuf_ioctl+0x132/0x1d0 home/zzzrrll/tmp/kf_src/linux-7.3-rc2/drivers/dma-buf/udmabuf.c:496 vfs_ioctl home/zzzrrll/tmp/kf_src/linux-7.3-rc2/fs/ioctl.c:51 [inline] __do_sys_ioctl home/zzzrrll/tmp/kf_src/linux-7.3-rc2/fs/ioctl.c:597 [inline] __se_sys_ioctl+0xbc/0x130 home/zzzrrll/tmp/kf_src/linux-7.3-rc2/fs/ioctl.c:583 do_syscall_x64 home/zzzrrll/tmp/kf_src/linux-7.3-rc2/arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x12b/0x350 home/zzzrrll/tmp/kf_src/linux-7.3-rc2/arch/x86/entry/syscall_64.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x590d6d Code: 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007fc89ae44fd8 EFLAGS: 00000216 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 0000000000611e7f RCX: 0000000000590d6d RDX: 00002000000023c0 RSI: 0000000040187542 RDI: 000000000000000a RBP: 00007fc89ae45010 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000216 R12: 00007fc89ae45640 R13: 000000000000000b R14: 0000000000528d40 R15: 00007fc89ae25000 </TASK> ---[ end trace 0000000000000000 ]--- ---