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commit f23a5350e43c810ca36b26d4ed4ecd9a08686f47 upstream. The ib_write_umad() is protected by taking the umad file mutex. However, it accesses file->port->ib_dev -- which is protected only by the port's mutex (field file_mutex). The ib_umad_remove_one() calls ib_umad_kill_port() which sets port->ib_dev to NULL under the port mutex (NOT the file mutex). It then sets the mad agent to "dead" under the umad file mutex. This is a race condition -- because there is a window where port->ib_dev is NULL, while the agent is not "dead". As a result, we saw stack traces like: [16490.678059] BUG: unable to handle kernel NULL pointer dereference at 00000000000000b0 [16490.678246] IP: ib_umad_write+0x29c/0xa3a [ib_umad] [16490.678333] PGD 0 P4D 0 [16490.678404] Oops: 0000 [#1] SMP PTI [16490.678466] Modules linked in: rdma_ucm(OE) ib_ucm(OE) rdma_cm(OE) iw_cm(OE) ib_ipoib(OE) ib_cm(OE) ib_uverbs(OE) ib_umad(OE) mlx4_en(OE) ptp pps_core mlx4_ib(OE-) ib_core(OE) mlx4_core(OE) mlx_compat (OE) memtrack(OE) devlink mst_pciconf(OE) mst_pci(OE) netconsole nfsv3 nfs_acl nfs lockd grace fscache cfg80211 rfkill esp6_offload esp6 esp4_offload esp4 sunrpc kvm_intel kvm ppdev parport_pc irqbypass parport joydev i2c_piix4 virtio_balloon cirrus drm_kms_helper ttm drm e1000 serio_raw virtio_pci virtio_ring virtio ata_generic pata_acpi qemu_fw_cfg [last unloaded: mlxfw] [16490.679202] CPU: 4 PID: 3115 Comm: sminfo Tainted: G OE 4.14.13-300.fc27.x86_64 #1 [16490.679339] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu2 04/01/2014 [16490.679477] task: ffff9cf753890000 task.stack: ffffaf70c26b0000 [16490.679571] RIP: 0010:ib_umad_write+0x29c/0xa3a [ib_umad] [16490.679664] RSP: 0018:ffffaf70c26b3d90 EFLAGS: 00010202 [16490.679747] RAX: 0000000000000010 RBX: ffff9cf75610fd80 RCX: 0000000000000000 [16490.679856] RDX: 0000000000000001 RSI: 00007ffdf2bfd714 RDI: ffff9cf6bb2a9c00 In the above trace, ib_umad_write is trying to dereference the NULL file->port->ib_dev pointer. Fix this by using the agent's device pointer (the device field in struct ib_mad_agent) -- which IS protected by the umad file mutex. Fixes: 44c58487d51a ("IB/core: Define 'ib' and 'roce' rdma_ah_attr types") Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il> Signed-off-by: Leon Romanovsky <leon@kernel.org> Signed-off-by: Jason Gunthorpe <jgg@mellanox.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.