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misc: fastrpc: fix double-free in fastrpc_map_attach() error path

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map->table is assigned right after dma_buf_map_attachment_unlocked()
succeeds. The two failure checks that follow, the len > map->size test
and, where subsystem VMIDs are configured, a failed qcom_scm_assign_mem(),
jump to map_err with map->table already set.

map_err manually calls dma_buf_detach() and dma_buf_put() and then falls
through to fastrpc_map_put(). Since that change the error path tail is
fastrpc_map_put() -> fastrpc_free_map(), and fastrpc_free_map() already
unmaps, detaches and puts the dma-buf whenever map->table is set.
The two operations therefore run twice: the second dma_buf_put() drops an
extra reference on map->buf, and dma_buf_unmap_attachment_unlocked()
dereferences the map->attach already freed by the manual dma_buf_detach().
kref_init() sets the refcount to 1 with no intervening get, so the final
fastrpc_map_put() frees the map synchronously and the redundant cleanup is
deterministic.

The len > map->size branch is reachable by an unprivileged process via
FASTRPC_IOCTL_MEM_MAP with an fd whose dma-buf is smaller than the
requested length, before any DSP invocation.

Route both map->table-is-set failure branches to get_err instead of
map_err, so fastrpc_free_map() is the single owner of the
unmap/detach/put sequence. map_err is retained for the
dma_buf_map_attachment_unlocked() failure, which is reached with
map->table still NULL and an attachment that fastrpc_free_map() will not
clean up, so its dma_buf_detach()/dma_buf_put() must still run manually.

Fixes: 334f1a1cbe ("misc: fastrpc: Use fastrpc_map_put in fastrpc_map_create on fail")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Yifei Gao <gyf161023@gmail.com>
Reviewed-by: Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>
Signed-off-by: Srinivas Kandagatla <srini@kernel.org>
Link: https://patch.msgid.link/20261002101220.1084101-2-srinivas.kandagatla@oss.qualcomm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Yifei Gao 2026-10-02 11:12:19 +01:00 committed by Greg Kroah-Hartman
parent 4bfc44cd14
commit 09fa66ec1b
1 changed files with 2 additions and 2 deletions
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4
drivers/misc/fastrpc.c
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@ -927,7 +927,7 @@ static int fastrpc_map_attach(struct fastrpc_user *fl, int fd,
dev_dbg(sess->dev, "Bad size passed len 0x%llx map size 0x%llx\n",
len, map->size);
err = -EINVAL;
goto map_err;
goto get_err;
}
map->va = sg_virt(map->table->sgl);
map->len = len;
@ -950,7 +950,7 @@ static int fastrpc_map_attach(struct fastrpc_user *fl, int fd,
dev_err(sess->dev,
"Failed to assign memory with dma_addr %pad size 0x%llx err %d\n",
&map->dma_addr, map->len, err);
goto map_err;
goto get_err;
}
}
spin_lock(&fl->lock);