From: Showrya M N <[email protected]> [ Upstream commit 3ea3a256ed81f95ab0f3281a0e234b01a9cae605 ]
In case of an ib_fast_reg_mr allocation failure during iSER setup, the machine hits a panic because iscsi_conn->dd_data is initialized unconditionally, even when no memory is allocated (dd_size == 0). This leads invalid pointer dereference during connection teardown. Fix by setting iscsi_conn->dd_data only if memory is actually allocated. Panic trace: ------------ iser: iser_create_fastreg_desc: Failed to allocate ib_fast_reg_mr err=-12 iser: iser_alloc_rx_descriptors: failed allocating rx descriptors / data buffers BUG: unable to handle page fault for address: fffffffffffffff8 RIP: 0010:swake_up_locked.part.5+0xa/0x40 Call Trace: complete+0x31/0x40 iscsi_iser_conn_stop+0x88/0xb0 [ib_iser] iscsi_stop_conn+0x66/0xc0 [scsi_transport_iscsi] iscsi_if_stop_conn+0x14a/0x150 [scsi_transport_iscsi] iscsi_if_rx+0x1135/0x1834 [scsi_transport_iscsi] ? netlink_lookup+0x12f/0x1b0 ? netlink_deliver_tap+0x2c/0x200 netlink_unicast+0x1ab/0x280 netlink_sendmsg+0x257/0x4f0 ? _copy_from_user+0x29/0x60 sock_sendmsg+0x5f/0x70 Signed-off-by: Showrya M N <[email protected]> Signed-off-by: Potnuri Bharat Teja <[email protected]> Link: https://lore.kernel.org/r/[email protected] Reviewed-by: Chris Leech <[email protected]> Signed-off-by: Martin K. Petersen <[email protected]> Signed-off-by: Sasha Levin <[email protected]> --- LLM Generated explanations, may be completely bogus: Now I see the pattern clearly! When `iscsi_alloc_conn` is called with `dd_size = 0`: - It allocates only `sizeof(*conn)` (no extra space) - It sets `conn->dd_data = NULL` (because dd_size is 0, the condition `if (dd_size)` is false) But in the original code in `iscsi_conn_setup()`, it was unconditionally setting: ```c conn->dd_data = cls_conn->dd_data + sizeof(*conn); ``` This would set `conn->dd_data` to point past the allocated memory when `dd_size = 0`, leading to the panic when the iSER driver tries to dereference it in `iscsi_iser_conn_stop()`. **Backport Status: YES** This commit should definitely be backported to stable kernel trees for the following reasons: 1. **Critical Bug Fix**: This fixes a kernel panic/crash that occurs during iSCSI/iSER connection teardown when memory allocation fails. The panic trace shows a page fault at address `fffffffffffffff8`, which is clearly an invalid pointer dereference. 2. **Real-World Impact**: The bug triggers when `ib_fast_reg_mr` allocation fails during iSER setup, which can happen under memory pressure. This leads to a system crash during error recovery, turning a recoverable allocation failure into a fatal kernel panic. 3. **Small and Contained Fix**: The fix is minimal - just adding a single conditional check: ```c if (dd_size) conn->dd_data = cls_conn->dd_data + sizeof(*conn); ``` This only affects the initialization path when `dd_size = 0`. 4. **No Architectural Changes**: This is a straightforward bug fix that doesn't introduce new features or change any architecture. It simply prevents setting an invalid pointer when no driver-specific data is allocated. 5. **Clear Root Cause**: The issue is well-understood: when drivers like iSER pass `dd_size = 0` to `iscsi_conn_setup()`, the code was unconditionally calculating a pointer past the allocated memory. During teardown, accessing this invalid pointer causes the panic. 6. **Minimal Risk**: The change only affects the case where `dd_size = 0`, which is specifically the iSER driver's usage pattern. Other drivers that pass non-zero `dd_size` values are unaffected. 7. **Follows Stable Rules**: This meets all stable kernel criteria: - Fixes a real bug that users can hit - Fix is already upstream (has proper sign-offs and review) - Small change (2 lines) - Obviously correct - Doesn't add new features The commit prevents a kernel panic during error handling in the iSCSI/iSER subsystem, making it an important stability fix that should be backported to all maintained stable kernels that include the iSER driver. drivers/scsi/libiscsi.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/scsi/libiscsi.c b/drivers/scsi/libiscsi.c index 392d57e054db..c9f410c50978 100644 --- a/drivers/scsi/libiscsi.c +++ b/drivers/scsi/libiscsi.c @@ -3185,7 +3185,8 @@ iscsi_conn_setup(struct iscsi_cls_session *cls_session, int dd_size, return NULL; conn = cls_conn->dd_data; - conn->dd_data = cls_conn->dd_data + sizeof(*conn); + if (dd_size) + conn->dd_data = cls_conn->dd_data + sizeof(*conn); conn->session = session; conn->cls_conn = cls_conn; conn->c_stage = ISCSI_CONN_INITIAL_STAGE; -- 2.39.5 -- You received this message because you are subscribed to the Google Groups "open-iscsi" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/d/msgid/open-iscsi/20250805130945.471732-56-sashal%40kernel.org.
