Re: [syzbot] [netfs?] BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write

[syzbot <syzbot+7227db0fbac9f348dba0@syzkaller.appspotmail.com>]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

lost connection to test machine



[   53.006729][   T40] audit: type=1400 audit(1772844781.220:61): avc:  denied  { siginh } for  pid=5916 comm="sh" scontext=system_u:system_r:sshd_t tcontext=root:sysadm_r:sysadm_t tclass=process permissive=1
Warning: Permanently added '[localhost]:6261' (ED25519) to the list of known hosts.
[   59.362394][   T40] audit: type=1400 audit(1772844787.600:62): avc:  denied  { execute } for  pid=5934 comm="sh" name="syz-execprog" dev="sda1" ino=2020 scontext=root:sysadm_r:sysadm_t tcontext=root:object_r:etc_runtime_t tclass=file permissive=1
[   59.370350][   T40] audit: type=1400 audit(1772844787.600:63): avc:  denied  { execute_no_trans } for  pid=5934 comm="sh" path="/syz-execprog" dev="sda1" ino=2020 scontext=root:sysadm_r:sysadm_t tcontext=root:object_r:etc_runtime_t tclass=file permissive=1
qemu-system-x86_64: ahci: PRDT length for NCQ command (0x0) is smaller than the requested size (0x276000)
[   60.287164][ T1115] ata1.00: Read log 0x10 page 0x00 failed, Emask 0x1
[   60.290289][ T1115] ata1: failed to read log page 10h (errno=-5)
[   60.293027][ T1115] ata1.00: exception Emask 0x1 SAct 0x18000000 SErr 0x0 action 0x0
[   60.296801][ T1115] ata1.00: irq_stat 0x41000000
[   60.298945][ T1115] ata1.00: failed command: WRITE FPDMA QUEUED
[   60.301653][ T1115] ata1.00: cmd 61/b0:d8:86:ad:04/13:00:00:00:00/40 tag 27 ncq dma 2580480 ou
[   60.301653][ T1115]          res 50/00:00:00:00:00/00:00:00:00:00/00 Emask 0x1 (device error)
[   60.309312][ T1115] ata1.00: status: { DRDY }
[   60.311350][ T1115] ata1.00: failed command: WRITE FPDMA QUEUED
[   60.314078][ T1115] ata1.00: cmd 61/a8:e0:36:c1:04/06:00:00:00:00/40 tag 28 ncq dma 872448 out
[   60.314078][ T1115]          res 50/00:00:00:00:00/00:00:00:00:00/00 Emask 0x1 (device error)
[   60.321656][ T1115] ata1.00: status: { DRDY }
[   60.325837][ T1115] ata1.00: configured for UDMA/100
[   60.328869][ T1115] ata1: EH complete
qemu-system-x86_64: ahci: PRDT length for NCQ command (0x0) is smaller than the requested size (0x306000)
2026/03/07 00:53:09 parsed 1 programs
[   60.882101][   T40] audit: type=1400 audit(1772844789.120:64): avc:  denied  { node_bind } for  pid=5934 comm="syz-execprog" saddr=::1 scontext=root:sysadm_r:sysadm_t tcontext=system_u:object_r:node_t tclass=tcp_socket permissive=1
[   63.061673][   T40] audit: type=1400 audit(1772844791.300:65): avc:  denied  { mounton } for  pid=5944 comm="syz-executor" path="/syzcgroup/unified" dev="sda1" ino=2023 scontext=root:sysadm_r:sysadm_t tcontext=root:object_r:root_t tclass=dir permissive=1
[   63.072219][   T40] audit: type=1400 audit(1772844791.310:66): avc:  denied  { mount } for  pid=5944 comm="syz-executor" name="/" dev="cgroup2" ino=1 scontext=root:sysadm_r:sysadm_t tcontext=system_u:object_r:cgroup_t tclass=filesystem permissive=1
[   63.074421][ T5944] cgroup: Unknown subsys name 'net'
[   63.086127][   T40] audit: type=1400 audit(1772844791.330:67): avc:  denied  { unmount } for  pid=5944 comm="syz-executor" scontext=root:sysadm_r:sysadm_t tcontext=system_u:object_r:cgroup_t tclass=filesystem permissive=1
[   63.204323][ T5944] cgroup: Unknown subsys name 'cpuset'
[   63.211220][ T5944] cgroup: Unknown subsys name 'rlimit'
[   63.354811][   T40] audit: type=1400 audit(1772844791.590:68): avc:  denied  { setattr } for  pid=5944 comm="syz-executor" name="raw-gadget" dev="devtmpfs" ino=849 scontext=root:sysadm_r:sysadm_t tcontext=system_u:object_r:device_t tclass=chr_file permissive=1
[   63.362722][   T40] audit: type=1400 audit(1772844791.590:69): avc:  denied  { create } for  pid=5944 comm="syz-executor" scontext=root:sysadm_r:sysadm_t tcontext=root:sysadm_r:sysadm_t tclass=netlink_generic_socket permissive=1
[   63.371542][   T40] audit: type=1400 audit(1772844791.590:70): avc:  denied  { write } for  pid=5944 comm="syz-executor" scontext=root:sysadm_r:sysadm_t tcontext=root:sysadm_r:sysadm_t tclass=netlink_generic_socket permissive=1
[   63.379823][   T40] audit: type=1400 audit(1772844791.590:71): avc:  denied  { read } for  pid=5944 comm="syz-executor" scontext=root:sysadm_r:sysadm_t tcontext=root:sysadm_r:sysadm_t tclass=netlink_generic_socket permissive=1
[   76.290044][ T1418] ieee802154 phy0 wpan0: encryption failed: -22
[   76.292902][ T1418] ieee802154 phy1 wpan1: encryption failed: -22
[   86.527671][   T71] cfg80211: failed to load regulatory.db
[   90.406172][ T1115] ata1.00: exception Emask 0x0 SAct 0x8000000 SErr 0x0 action 0x6 frozen
[   90.408914][ T1115] ata1.00: failed command: WRITE FPDMA QUEUED
[   90.410920][ T1115] ata1.00: cmd 61/30:d8:06:29:05/18:00:00:00:00/40 tag 27 ncq dma 3170304 ou
[   90.410920][ T1115]          res 40/00:00:00:00:00/00:00:00:00:00/00 Emask 0x4 (timeout)
[   90.417891][ T1115] ata1.00: status: { DRDY }
[   90.419868][ T1115] ata1: hard resetting link
[   90.740475][ T1115] ata1: SATA link up 1.5 Gbps (SStatus 113 SControl 300)
[   90.744117][ T1115] ata1.00: configured for UDMA/100
[   90.746150][ T1115] ata1: EH complete
[   90.797641][ T5947] SELinux:  Context root:object_r:swapfile_t is not valid (left unmapped).
[   90.802207][   T40] kauditd_printk_skb: 6 callbacks suppressed
[   90.802221][   T40] audit: type=1400 audit(1772844819.040:78): avc:  denied  { relabelto } for  pid=5947 comm="mkswap" name="swap-file" dev="sda1" ino=2026 scontext=root:sysadm_r:sysadm_t tcontext=system_u:object_r:unlabeled_t tclass=file permissive=1 trawcon="root:object_r:swapfile_t"
qemu-system-x86_64: ahci: PRDT length for NCQ command (0x0) is smaller than the requested size (0xa6000)
[   90.886300][   T40] audit: type=1400 audit(1772844819.120:79): avc:  denied  { write } for  pid=5947 comm="mkswap" path="/swap-file" dev="sda1" ino=2026 scontext=root:sysadm_r:sysadm_t tcontext=system_u:object_r:unlabeled_t tclass=file permissive=1 trawcon="root:object_r:swapfile_t"
[   90.937311][ T1115] ata1.00: Read log 0x10 page 0x00 failed, Emask 0x1
[   90.940273][ T1115] ata1: failed to read log page 10h (errno=-5)
[   90.943034][ T1115] ata1.00: exception Emask 0x1 SAct 0x4000 SErr 0x0 action 0x0
[   90.946430][ T1115] ata1.00: irq_stat 0x41000008
[   90.948570][ T1115] ata1.00: failed command: WRITE FPDMA QUEUED
[   90.951219][ T1115] ata1.00: cmd 61/30:70:46:90:05/05:00:00:00:00/40 tag 14 ncq dma 679936 out
[   90.951219][ T1115]          res 50/04:00:00:00:00/00:00:00:00:00/00 Emask 0x1 (device error)
[   90.958887][ T1115] ata1.00: status: { DRDY }
[   90.960867][ T1115] ata1.00: error: { ABRT }
[   90.963944][ T1115] ata1.00: configured for UDMA/100
[   90.966577][ T1115] ata1: EH complete
qemu-system-x86_64: ahci: PRDT length for NCQ command (0x0) is smaller than the requested size (0x400000)
[   91.007150][ T1115] ata1.00: Read log 0x10 page 0x00 failed, Emask 0x1
[   91.010097][ T1115] ata1: failed to read log page 10h (errno=-5)
[   91.012787][ T1115] ata1.00: NCQ disabled due to excessive errors
[   91.015506][ T1115] ata1.00: exception Emask 0x1 SAct 0x600000 SErr 0x0 action 0x0
[   91.019092][ T1115] ata1.00: irq_stat 0x41000000
[   91.020807][ T1115] ata1.00: failed command: WRITE FPDMA QUEUED
[   91.022931][ T1115] ata1.00: cmd 61/00:a8:76:95:05/20:00:00:00:00/40 tag 21 ncq dma 4194304 ou
[   91.022931][ T1115]          res 50/04:00:00:00:00/00:00:00:00:00/00 Emask 0x1 (device error)
[   91.029236][ T1115] ata1.00: status: { DRDY }
[   91.030908][ T1115] ata1.00: error: { ABRT }
[   91.032434][ T1115] ata1.00: failed command: WRITE FPDMA QUEUED
[   91.034457][ T1115] ata1.00: cmd 61/30:b0:46:90:05/05:00:00:00:00/40 tag 22 ncq dma 679936 out
[   91.034457][ T1115]          res 50/04:01:00:00:00/00:00:00:00:00/00 Emask 0x1 (device error)
[   91.041746][ T1115] ata1.00: status: { DRDY }
[   91.043252][ T1115] ata1.00: error: { ABRT }
[   91.045632][ T1115] ata1.00: configured for UDMA/100
[   91.048480][ T1115] ata1: EH complete
qemu-system-x86_64: hw/ide/core.c:934: ide_dma_cb: Assertion `prep_size >= 0 && prep_size <= n * 512' failed.
Connection to localhost closed by remote host.


syzkaller build log:
go env (err=<nil>)
AR='ar'
CC='gcc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='g++'
GCCGO='gccgo'
GO111MODULE='auto'
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/syzkaller/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/syzkaller/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build1814019681=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/syzkaller/jobs/linux/gopath/src/github.com/google/syzkaller/go.mod'
GOMODCACHE='/syzkaller/jobs/linux/gopath/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/syzkaller/jobs/linux/gopath'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/syzkaller/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.24.4'
GOWORK=''
PKG_CONFIG='pkg-config'

git status (err=<nil>)
HEAD detached at d20b04c80a0
nothing to commit, working tree clean


tput: No value for $TERM and no -T specified
tput: No value for $TERM and no -T specified
Makefile:31: run command via tools/syz-env for best compatibility, see:
Makefile:32: https://github.com/google/syzkaller/blob/master/docs/contributing.md#using-syz-env
go list -f '{{.Stale}}' -ldflags="-s -w -X github.com/google/syzkaller/prog.GitRevision=d20b04c80a01e68026299511a6ba77cc67a198f5 -X github.com/google/syzkaller/prog.gitRevisionDate=20260305-101922"  ./sys/syz-sysgen | grep -q false || go install -ldflags="-s -w -X github.com/google/syzkaller/prog.GitRevision=d20b04c80a01e68026299511a6ba77cc67a198f5 -X github.com/google/syzkaller/prog.gitRevisionDate=20260305-101922"  ./sys/syz-sysgen
make .descriptions
tput: No value for $TERM and no -T specified
tput: No value for $TERM and no -T specified
Makefile:31: run command via tools/syz-env for best compatibility, see:
Makefile:32: https://github.com/google/syzkaller/blob/master/docs/contributing.md#using-syz-env
bin/syz-sysgen
touch .descriptions
GOOS=linux GOARCH=amd64 go build -ldflags="-s -w -X github.com/google/syzkaller/prog.GitRevision=d20b04c80a01e68026299511a6ba77cc67a198f5 -X github.com/google/syzkaller/prog.gitRevisionDate=20260305-101922"  -o ./bin/linux_amd64/syz-execprog github.com/google/syzkaller/tools/syz-execprog
mkdir -p ./bin/linux_amd64
g++ -o ./bin/linux_amd64/syz-executor executor/executor.cc \
	-m64 -O2 -pthread -Wall -Werror -Wparentheses -Wunused-const-variable -Wframe-larger-than=16384 -Wno-stringop-overflow -Wno-array-bounds -Wno-format-overflow -Wno-unused-but-set-variable -Wno-unused-command-line-argument -static-pie -std=c++17 -I. -Iexecutor/_include   -DGOOS_linux=1 -DGOARCH_amd64=1 \
	-DHOSTGOOS_linux=1 -DGIT_REVISION=\"d20b04c80a01e68026299511a6ba77cc67a198f5\"
/usr/bin/ld: /tmp/ccZswRL1.o: in function `Connection::Connect(char const*, char const*)':
executor.cc:(.text._ZN10Connection7ConnectEPKcS1_[_ZN10Connection7ConnectEPKcS1_]+0x386): warning: Using 'gethostbyname' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
./tools/check-syzos.sh 2>/dev/null



Tested on:

commit:         325a118c Merge tag 'pci-v7.0-fixes-3' of git://git.ker..
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=976ba5a93c4add9e
dashboard link: https://syzkaller.appspot.com/bug?extid=7227db0fbac9f348dba0
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
patch:          https://syzkaller.appspot.com/x/patch.diff?x=16cbfb5a580000