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.
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.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | |||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
|
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| Linux | Linux | affected |
|
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Advisories
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Fixes
Solution
No solution given by the vendor.
Workaround
No workaround given by the vendor.
References
History
Sun, 19 Jul 2026 15:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | 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. | |
| Title | scsi: target: iscsi: Fix CRC overread and double-free in iscsit_handle_text_cmd() | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
|
Projects
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MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-07-19T14:55:00.803Z
Reserved: 2026-07-19T07:54:57.018Z
Link: CVE-2026-63888
Vulnrichment
No data.
NVD
No data.
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.