CVE-2023-54112kcm: Fix memory leak in error path of kcm_sendmsg()

Official description

In the Linux kernel, the following vulnerability has been resolved: kcm: Fix memory leak in error path of kcm_sendmsg() syzbot reported a memory leak like below: BUG: memory leak unreferenced object 0xffff88810b088c00 (size 240): comm "syz-executor186", pid 5012, jiffies 4294943306 (age 13.680s) hex dump (first 32 bytes): 00 89 08 0b 81 88 ff ff 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ backtrace: [<ffffffff83e5d5ff>] __alloc_skb+0x1ef/0x230 net/core/skbuff.c:634 [<ffffffff84606e59>] alloc_skb include/linux/skbuff.h:1289 [inline] [<ffffffff84606e59>] kcm_sendmsg+0x269/0x1050 net/kcm/kcmsock.c:815 [<ffffffff83e479c6>] sock_sendmsg_nosec net/socket.c:725 [inline] [<ffffffff83e479c6>] sock_sendmsg+0x56/0xb0 net/socket.c:748 [<ffffffff83e47f55>] ____sys_sendmsg+0x365/0x470 net/socket.c:2494 [<ffffffff83e4c389>] ___sys_sendmsg+0xc9/0x130 net/socket.c:2548 [<ffffffff83e4c536>] __sys_sendmsg+0xa6/0x120 net/socket.c:2577 [<ffffffff84ad7bb8>] do_syscall_x64 arch/x86/entry/common.c:50 [inline] [<ffffffff84ad7bb8>] do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80 [<ffffffff84c0008b>] entry_SYSCALL_64_after_hwframe+0x63/0xcd In kcm_sendmsg(), kcm_tx_msg(head)->last_skb is used as a cursor to append newly allocated skbs to 'head'. If some bytes are copied, an error occurred, and jumped to out_error label, 'last_skb' is left unmodified. A later kcm_sendmsg() will use an obsoleted 'last_skb' reference, corrupting the 'head' frag_list and causing the leak. This patch fixes this issue by properly updating the last allocated skb in 'last_skb'.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/8dc7eb757b1652b82725f32e0c89a1e9f6c0e13b
• https://git.kernel.org/stable/c/5e5554389397e98fafb9efe395d8b4830dd5f042
• https://git.kernel.org/stable/c/479c71cda14b3c3a6515773faa39055333eaa2b7
• https://git.kernel.org/stable/c/33db24ad811b3576a0c2f8862506763f2be925b0
• https://git.kernel.org/stable/c/97275339c34cfbccd65e87bc38fd910ae66c48ba
• https://git.kernel.org/stable/c/16989de75497574b5fafd174c0c233d5a86858b7
• https://git.kernel.org/stable/c/af8085e0fc3207ecbf8b9e7a635c790e36d058c6
• https://git.kernel.org/stable/c/c821a88bd720b0046433173185fd841a100d44ad