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

Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code.

Affected Software

Extended Description

The use of previously-freed memory can have any number of adverse consequences, ranging from the corruption of valid data to the execution of arbitrary code, depending on the instantiation and timing of the flaw. The simplest way data corruption may occur involves the system’s reuse of the freed memory. Use-after-free errors have two common and sometimes overlapping causes:

In this scenario, the memory in question is allocated to another pointer validly at some point after it has been freed. The original pointer to the freed memory is used again and points to somewhere within the new allocation. As the data is changed, it corrupts the validly used memory; this induces undefined behavior in the process. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.

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