path: root/Documentation
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authorRob Clark <>2012-03-19 16:42:49 -0500
committerSumit Semwal <>2012-03-26 11:33:22 +0530
commitfbb231e1a98cb0360b681b6a6195a619e98d7077 (patch)
treec7a3bd8975fc2d6a7e2ab25df02402a489b350ac /Documentation
parentb0b40f24848440aa65418532fe97d8d46acceb3d (diff)
dma-buf: document fd flags and O_CLOEXEC requirement
Otherwise subsystems will get this wrong and end up with a second export ioctl with the flag and O_CLOEXEC support added. Signed-off-by: Rob Clark <> Reviewed-by: Daniel Vetter <> Signed-off-by: Sumit Semwal <>
Diffstat (limited to 'Documentation')
1 files changed, 18 insertions, 0 deletions
diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-buf-sharing.txt
index 9f3aeeffd608..3bbd5c51605a 100644
--- a/Documentation/dma-buf-sharing.txt
+++ b/Documentation/dma-buf-sharing.txt
@@ -319,6 +319,24 @@ Miscellaneous notes
- Any exporters or users of the dma-buf buffer sharing framework must have
a 'select DMA_SHARED_BUFFER' in their respective Kconfigs.
+- In order to avoid fd leaks on exec, the FD_CLOEXEC flag must be set
+ on the file descriptor. This is not just a resource leak, but a
+ potential security hole. It could give the newly exec'd application
+ access to buffers, via the leaked fd, to which it should otherwise
+ not be permitted access.
+ The problem with doing this via a separate fcntl() call, versus doing it
+ atomically when the fd is created, is that this is inherently racy in a
+ multi-threaded app[3]. The issue is made worse when it is library code
+ opening/creating the file descriptor, as the application may not even be
+ aware of the fd's.
+ To avoid this problem, userspace must have a way to request O_CLOEXEC
+ flag be set when the dma-buf fd is created. So any API provided by
+ the exporting driver to create a dmabuf fd must provide a way to let
+ userspace control setting of O_CLOEXEC flag passed in to dma_buf_fd().
[1] struct dma_buf_ops in include/linux/dma-buf.h
[2] All interfaces mentioned above defined in include/linux/dma-buf.h