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misc: fastrpc: avoid double fput() on failed usercopy

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If the copy back to userland fails for the FASTRPC_IOCTL_ALLOC_DMA_BUFF
ioctl(), we shouldn't assume that 'buf->dmabuf' is still valid. In fact,
dma_buf_fd() called fd_install() before, i.e. "consumed" one reference,
leaving us with none.

Calling dma_buf_put() will therefore put a reference we no longer own,
leading to a valid file descritor table entry for an already released
'file' object which is a straight use-after-free.

Simply avoid calling dma_buf_put() and rely on the process exit code to
do the necessary cleanup, if needed, i.e. if the file descriptor is
still valid.

Fixes: 6cffd79504 ("misc: fastrpc: Add support for dmabuf exporter")
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Mathias Krause <minipli@grsecurity.net>
Link: https://lore.kernel.org/r/20220127130218.809261-1-minipli@grsecurity.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Mathias Krause 2022-01-27 14:02:18 +01:00 committed by Greg Kroah-Hartman
parent 26291c54e1
commit 46963e2e06
1 changed files with 8 additions and 1 deletions
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9
drivers/misc/fastrpc.c
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@ -1288,7 +1288,14 @@ static int fastrpc_dmabuf_alloc(struct fastrpc_user *fl, char __user *argp)
}
if (copy_to_user(argp, &bp, sizeof(bp))) {
dma_buf_put(buf->dmabuf);
/*
* The usercopy failed, but we can't do much about it, as
* dma_buf_fd() already called fd_install() and made the
* file descriptor accessible for the current process. It
* might already be closed and dmabuf no longer valid when
* we reach this point. Therefore "leak" the fd and rely on
* the process exit path to do any required cleanup.
*/
return -EFAULT;
}