From: Jann Horn Date: Wed, 4 Dec 2024 16:26:19 +0000 (+0100) Subject: udmabuf: fix racy memfd sealing check X-Git-Tag: v6.12.7~16 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=93f08e5c393fa648a2e3e7ad2d37dd6a16cd726d;p=thirdparty%2Fkernel%2Fstable.git udmabuf: fix racy memfd sealing check commit 9cb189a882738c1d28b349d4e7c6a1ef9b3d8f87 upstream. The current check_memfd_seals() is racy: Since we first do check_memfd_seals() and then udmabuf_pin_folios() without holding any relevant lock across both, F_SEAL_WRITE can be set in between. This is problematic because we can end up holding pins to pages in a write-sealed memfd. Fix it using the inode lock, that's probably the easiest way. In the future, we might want to consider moving this logic into memfd, especially if anyone else wants to use memfd_pin_folios(). Reported-by: Julian Orth Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219106 Closes: https://lore.kernel.org/r/CAG48ez0w8HrFEZtJkfmkVKFDhE5aP7nz=obrimeTgpD+StkV9w@mail.gmail.com Fixes: fbb0de795078 ("Add udmabuf misc device") Cc: stable@vger.kernel.org Signed-off-by: Jann Horn Acked-by: Joel Fernandes (Google) Acked-by: Vivek Kasireddy Signed-off-by: Vivek Kasireddy Link: https://patchwork.freedesktop.org/patch/msgid/20241204-udmabuf-fixes-v2-1-23887289de1c@google.com Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c index 614df433c4513..c2e2277621529 100644 --- a/drivers/dma-buf/udmabuf.c +++ b/drivers/dma-buf/udmabuf.c @@ -394,14 +394,19 @@ static long udmabuf_create(struct miscdevice *device, goto err; } + /* + * Take the inode lock to protect against concurrent + * memfd_add_seals(), which takes this lock in write mode. + */ + inode_lock_shared(file_inode(memfd)); ret = check_memfd_seals(memfd); - if (ret < 0) { - fput(memfd); - goto err; - } + if (ret) + goto out_unlock; ret = udmabuf_pin_folios(ubuf, memfd, list[i].offset, list[i].size); +out_unlock: + inode_unlock_shared(file_inode(memfd)); fput(memfd); if (ret) goto err;