CVE-2026-63888

Summary

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

scsi: target: iscsi: Fix CRC overread and double-free in iscsit_handle_text_cmd()

Two latent bugs in the Text-phase handler, both present since the original LIO integration in commit e48354ce078c ("iscsi-target: Add iSCSI fabric support for target v4.1"):

1. DataDigest CRC buffer overread (4 bytes past text_in).

   text_in is kzalloc()'d at ALIGN(payload_length, 4). rx_size is then incremented by ISCSI_CRC_LEN to make room for the received DataDigest in the iovec, but the same (now-bumped) rx_size is passed as the buffer length to iscsit_crc_buf():

   if (conn->conn_ops->DataDigest) {
           ...
           rx_size += ISCSI_CRC_LEN;
   }
   ...
   if (conn->conn_ops->DataDigest) {
           data_crc = iscsit_crc_buf(text_in, rx_size, 0, NULL);
   

   iscsit_crc_buf() walks rx_size bytes of text_in with crc32c(), so when DataDigest is negotiated it reads 4 bytes past the end of the text_in allocation. KASAN reproduces this directly on the unpatched mainline tree as slab-out-of-bounds in crc32c() called from the Text PDU path. The OOB bytes feed crc32c() and are then compared against the initiator-supplied checksum, so the value does not flow back to the attacker, but the kernel does read past the buffer on every Text PDU with DataDigest=CRC32C.

   Fix by passing the actual padded payload length (ALIGN(payload_length, 4)) that was used for the kzalloc().

2. Stale cmd->text_in_ptr re-free (double-free) on ERL>0 bad DataDigest drop.

   On DataDigest mismatch with ErrorRecoveryLevel > 0 the handler silently drops the PDU and lets the initiator plug the CmdSN gap:

           kfree(text_in);
           return 0;
   

   cmd->text_in_ptr still points at the freed buffer. The next Text Request on the same ITT re-enters iscsit_setup_text_cmd(), which unconditionally does

   kfree(cmd->text_in_ptr);
   cmd->text_in_ptr = NULL;
   

   freeing the same pointer a second time. Session teardown via iscsit_release_cmd() has the same shape and hits the same double-free if the connection is dropped before a second Text Request arrives.

   On an unmodified mainline tree the bug-1 CRC overread fires first on the initial valid Text Request and perturbs the subsequent state, so #4 was isolated by building a kernel with only the bug-1 hunk of this patch applied plus temporary printk() observability around the three relevant kfree() sites. The observability prints are not part of this patch. On that build, a three-PDU Text Request sequence after login produces two back-to-back splats:

   BUG: KASAN: double-free in iscsit_setup_text_cmd+0x??
   BUG: KASAN: double-free in iscsit_release_cmd+0x??
   

   showing the same pointer freed in the ERL>0 drop path and again in iscsit_setup_text_cmd() (next Text Request on the same ITT) and once more in iscsit_release_cmd() (session teardown). On distro kernels with CONFIG_SLAB_FREELIST_HARDENED=y (default) the double-free becomes a remote kernel BUG(); on non-hardened kernels it corrupts the slab freelist.

   Fix by clearing cmd->text_in_ptr after the kfree() in the ERL>0 drop path. With both hunks applied #4 is directly observable on the stock tree without observability printks; fixing bug-1 alone would mask #4 less, not more, so the hunks are submitted together.

Both fixes are one-liners. The Text PDU state machine is unchanged and the wire protocol is unaffected.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/f7948af0dd03de84079dcd4dc215a69fd6fbb95d
• https://git.kernel.org/stable/c/badf178b76b0690851df00f4ca9cf2eb8eb0f963
• https://git.kernel.org/stable/c/6e22a1cdcc8277af4acc43710577157b77a02c5d
• https://git.kernel.org/stable/c/d3e9b79aa794f7a23e82de4d710e7d2df610e349
• https://git.kernel.org/stable/c/ec9f19d52074a191ed1756ed4a7d39fff1a2085c
• https://git.kernel.org/stable/c/89c81d1228c00fa6dd91de6c1c5aa1ef8a7875e3
• https://git.kernel.org/stable/c/5118ea225fe63b44207ba88047e4866e1ea43812
• https://git.kernel.org/stable/c/778c2ab142c625a8a8afa570e0f9b7873f445d99

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