Once FD_ADD() returns, the fd is live in the file descriptor table and a thread sharing that table can close() it before DMA_BUF_TRACE() runs. The close drops the last reference, __fput() frees the dma_buf, and the tracepoint then dereferences dmabuf to take dmabuf->name_lock -- slab-use-after-free.
Split FD_ADD() back into get_unused_fd_flags() + fd_install() and emit the tracepoint between them. While the fdtable slot is reserved with a NULL file pointer, a racing close() returns -EBADF without entering __fput(), so the dma_buf stays alive across the trace. Same approach as commit 2d76319c4cbb ("dma-buf: fix UAF in dma_buf_put() tracepoint").
This undoes the FD_ADD() conversion done in commit 34dfce523c90 ("dma: convert dma_buf_fd() to FD_ADD()"); FD_ADD() has no place to hook the tracepoint safely.
Reported-by: syzbot+7f4987d0afb97dd090cb@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=7f4987d0afb97dd090cb Fixes: 281a22631423 ("dma-buf: add some tracepoints to debug.") Cc: stable@vger.kernel.org # 7.0.x Signed-off-by: David Carlier devnexen@gmail.com --- drivers/dma-buf/dma-buf.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 71f37544a5c6..d504c636dc29 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -792,9 +792,13 @@ int dma_buf_fd(struct dma_buf *dmabuf, int flags) if (!dmabuf || !dmabuf->file) return -EINVAL;
- fd = FD_ADD(flags, dmabuf->file); + fd = get_unused_fd_flags(flags); + if (fd < 0) + return fd; + DMA_BUF_TRACE(trace_dma_buf_fd, dmabuf, fd);
+ fd_install(fd, dmabuf->file); return fd; } EXPORT_SYMBOL_NS_GPL(dma_buf_fd, "DMA_BUF");
On 5/23/26 20:14, David Carlier wrote:
Once FD_ADD() returns, the fd is live in the file descriptor table and a thread sharing that table can close() it before DMA_BUF_TRACE() runs. The close drops the last reference, __fput() frees the dma_buf, and the tracepoint then dereferences dmabuf to take dmabuf->name_lock -- slab-use-after-free.
Split FD_ADD() back into get_unused_fd_flags() + fd_install() and emit the tracepoint between them. While the fdtable slot is reserved with a NULL file pointer, a racing close() returns -EBADF without entering __fput(), so the dma_buf stays alive across the trace. Same approach as commit 2d76319c4cbb ("dma-buf: fix UAF in dma_buf_put() tracepoint").
This undoes the FD_ADD() conversion done in commit 34dfce523c90 ("dma: convert dma_buf_fd() to FD_ADD()"); FD_ADD() has no place to hook the tracepoint safely.
Reported-by: syzbot+7f4987d0afb97dd090cb@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=7f4987d0afb97dd090cb Fixes: 281a22631423 ("dma-buf: add some tracepoints to debug.") Cc: stable@vger.kernel.org # 7.0.x Signed-off-by: David Carlier devnexen@gmail.com
Reviewed-by: Christian König christian.koenig@amd.com
drivers/dma-buf/dma-buf.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 71f37544a5c6..d504c636dc29 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -792,9 +792,13 @@ int dma_buf_fd(struct dma_buf *dmabuf, int flags) if (!dmabuf || !dmabuf->file) return -EINVAL;
fd = FD_ADD(flags, dmabuf->file);
fd = get_unused_fd_flags(flags);if (fd < 0)return fd;DMA_BUF_TRACE(trace_dma_buf_fd, dmabuf, fd);fd_install(fd, dmabuf->file); return fd;} EXPORT_SYMBOL_NS_GPL(dma_buf_fd, "DMA_BUF"); -- 2.53.0
Hi David,
On Tue, 26 May 2026 at 00:25, Christian König christian.koenig@amd.com wrote:
On 5/23/26 20:14, David Carlier wrote:
Once FD_ADD() returns, the fd is live in the file descriptor table and a thread sharing that table can close() it before DMA_BUF_TRACE() runs. The close drops the last reference, __fput() frees the dma_buf, and the tracepoint then dereferences dmabuf to take dmabuf->name_lock -- slab-use-after-free.
Split FD_ADD() back into get_unused_fd_flags() + fd_install() and emit the tracepoint between them. While the fdtable slot is reserved with a NULL file pointer, a racing close() returns -EBADF without entering __fput(), so the dma_buf stays alive across the trace. Same approach as commit 2d76319c4cbb ("dma-buf: fix UAF in dma_buf_put() tracepoint").
This undoes the FD_ADD() conversion done in commit 34dfce523c90 ("dma: convert dma_buf_fd() to FD_ADD()"); FD_ADD() has no place to hook the tracepoint safely.
Reported-by: syzbot+7f4987d0afb97dd090cb@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=7f4987d0afb97dd090cb Fixes: 281a22631423 ("dma-buf: add some tracepoints to debug.") Cc: stable@vger.kernel.org # 7.0.x Signed-off-by: David Carlier devnexen@gmail.com
Reviewed-by: Christian König christian.koenig@amd.com
Thanks very much for the patch; applied to drm-misc-fixes.
drivers/dma-buf/dma-buf.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 71f37544a5c6..d504c636dc29 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -792,9 +792,13 @@ int dma_buf_fd(struct dma_buf *dmabuf, int flags) if (!dmabuf || !dmabuf->file) return -EINVAL;
fd = FD_ADD(flags, dmabuf->file);
fd = get_unused_fd_flags(flags);if (fd < 0)return fd;DMA_BUF_TRACE(trace_dma_buf_fd, dmabuf, fd);fd_install(fd, dmabuf->file); return fd;} EXPORT_SYMBOL_NS_GPL(dma_buf_fd, "DMA_BUF"); -- 2.53.0
Best, Sumit.
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Christian König -
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Sumit Semwal