CVE-2021-47068

In the Linux kernel, the following vulnerability has been resolved:

net/nfc: fix use-after-free llcp_sock_bind/connect

Commits 8a4cd82d (nfc: fix refcount leak in llcp_sock_connect()) and c33b1cc62 (nfc: fix refcount leak in llcp_sock_bind()) fixed a refcount leak bug in bind/connect but introduced a use-after-free if the same local is assigned to 2 different sockets.

This can be triggered by the following simple program: int sock1 = socket( AF_NFC, SOCK_STREAM, NFC_SOCKPROTO_LLCP ); int sock2 = socket( AF_NFC, SOCK_STREAM, NFC_SOCKPROTO_LLCP ); memset( &addr, 0, sizeof(struct sockaddr_nfc_llcp) ); addr.sa_family = AF_NFC; addr.nfc_protocol = NFC_PROTO_NFC_DEP; bind( sock1, (struct sockaddr*) &addr, sizeof(struct sockaddr_nfc_llcp) ) bind( sock2, (struct sockaddr*) &addr, sizeof(struct sockaddr_nfc_llcp) ) close(sock1); close(sock2);

Fix this by assigning NULL to llcp_sock->local after calling nfc_llcp_local_put.

This addresses CVE-2021-23134.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/18175fe17ae043a0b81e5d511f8817825784c299
• https://git.kernel.org/stable/c/18ae4a192a4496e48a5490b52812645d2413307c
• https://git.kernel.org/stable/c/26157c82ba756767b2bd66d28a71b1bc454447f6
• https://git.kernel.org/stable/c/374cdde4dcc9c909a60713abdbbf96d5e3e09f91
• https://git.kernel.org/stable/c/48fba458fe54cc2a980a05c13e6c19b8b2cfb610
• https://git.kernel.org/stable/c/6b7021ed36dabf29e56842e3408781cd3b82ef6e
• https://git.kernel.org/stable/c/c61760e6940dd4039a7f5e84a6afc9cdbf4d82b6
• https://git.kernel.org/stable/c/ccddad6dd28530e716448e594c9ca7c76ccd0570
• https://git.kernel.org/stable/c/e32352070bcac22be6ed8ab635debc280bb65b8c
• https://git.kernel.org/stable/c/18175fe17ae043a0b81e5d511f8817825784c299
• https://git.kernel.org/stable/c/18ae4a192a4496e48a5490b52812645d2413307c
• https://git.kernel.org/stable/c/26157c82ba756767b2bd66d28a71b1bc454447f6
• https://git.kernel.org/stable/c/374cdde4dcc9c909a60713abdbbf96d5e3e09f91
• https://git.kernel.org/stable/c/48fba458fe54cc2a980a05c13e6c19b8b2cfb610
• https://git.kernel.org/stable/c/6b7021ed36dabf29e56842e3408781cd3b82ef6e
• https://git.kernel.org/stable/c/c61760e6940dd4039a7f5e84a6afc9cdbf4d82b6
• https://git.kernel.org/stable/c/ccddad6dd28530e716448e594c9ca7c76ccd0570
• https://git.kernel.org/stable/c/e32352070bcac22be6ed8ab635debc280bb65b8c