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SandyWinterPaolo Abeni
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net/iucv: fix use after free in iucv_sock_close()
iucv_sever_path() is called from process context and from bh context. iucv->path is used as indicator whether somebody else is taking care of severing the path (or it is already removed / never existed). This needs to be done with atomic compare and swap, otherwise there is a small window where iucv_sock_close() will try to work with a path that has already been severed and freed by iucv_callback_connrej() called by iucv_tasklet_fn(). Example: [452744.123844] Call Trace: [452744.123845] ([<0000001e87f03880>] 0x1e87f03880) [452744.123966] [<00000000d593001e>] iucv_path_sever+0x96/0x138 [452744.124330] [<000003ff801ddbca>] iucv_sever_path+0xc2/0xd0 [af_iucv] [452744.124336] [<000003ff801e01b6>] iucv_sock_close+0xa6/0x310 [af_iucv] [452744.124341] [<000003ff801e08cc>] iucv_sock_release+0x3c/0xd0 [af_iucv] [452744.124345] [<00000000d574794e>] __sock_release+0x5e/0xe8 [452744.124815] [<00000000d5747a0c>] sock_close+0x34/0x48 [452744.124820] [<00000000d5421642>] __fput+0xba/0x268 [452744.124826] [<00000000d51b382c>] task_work_run+0xbc/0xf0 [452744.124832] [<00000000d5145710>] do_notify_resume+0x88/0x90 [452744.124841] [<00000000d5978096>] system_call+0xe2/0x2c8 [452744.125319] Last Breaking-Event-Address: [452744.125321] [<00000000d5930018>] iucv_path_sever+0x90/0x138 [452744.125324] [452744.125325] Kernel panic - not syncing: Fatal exception in interrupt Note that bh_lock_sock() is not serializing the tasklet context against process context, because the check for sock_owned_by_user() and corresponding handling is missing. Ideas for a future clean-up patch: A) Correct usage of bh_lock_sock() in tasklet context, as described in Link: https://lore.kernel.org/netdev/1280155406.2899.407.camel@edumazet-laptop/ Re-enqueue, if needed. This may require adding return values to the tasklet functions and thus changes to all users of iucv. B) Change iucv tasklet into worker and use only lock_sock() in af_iucv. Fixes: 7d316b9 ("af_iucv: remove IUCV-pathes completely") Reviewed-by: Halil Pasic <[email protected]> Signed-off-by: Alexandra Winter <[email protected]> Link: https://patch.msgid.link/[email protected] Signed-off-by: Paolo Abeni <[email protected]>
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net/iucv/af_iucv.c

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -335,8 +335,8 @@ static void iucv_sever_path(struct sock *sk, int with_user_data)
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struct iucv_sock *iucv = iucv_sk(sk);
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struct iucv_path *path = iucv->path;
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if (iucv->path) {
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iucv->path = NULL;
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/* Whoever resets the path pointer, must sever and free it. */
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if (xchg(&iucv->path, NULL)) {
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if (with_user_data) {
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low_nmcpy(user_data, iucv->src_name);
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high_nmcpy(user_data, iucv->dst_name);

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