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



[   52.755134][   T40] audit: type=1400 audit(1772843937.457:60): avc:  denied  { rlimitinh } for  pid=5908 comm="sh" scontext=system_u:system_r:sshd_t tcontext=root:sysadm_r:sysadm_t tclass=process permissive=1
[   52.762936][   T40] audit: type=1400 audit(1772843937.457:61): avc:  denied  { siginh } for  pid=5908 comm="sh" scontext=system_u:system_r:sshd_t tcontext=root:sysadm_r:sysadm_t tclass=process permissive=1
Warning: Permanently added '[localhost]:9893' (ED25519) to the list of known hosts.
[   59.078731][   T40] audit: type=1400 audit(1772843943.797:62): avc:  denied  { execute } for  pid=5928 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
[   59.085870][   T40] audit: type=1400 audit(1772843943.797:63): avc:  denied  { execute_no_trans } for  pid=5928 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 (0x99000)
[   59.742863][ T1116] ata1.00: Read log 0x10 page 0x00 failed, Emask 0x1
[   59.745980][ T1116] ata1: failed to read log page 10h (errno=-5)
[   59.748698][ T1116] ata1.00: exception Emask 0x1 SAct 0x40000001 SErr 0x0 action 0x0
[   59.752402][ T1116] ata1.00: irq_stat 0x41000000
[   59.754519][ T1116] ata1.00: failed command: WRITE FPDMA QUEUED
[   59.757324][ T1116] ata1.00: cmd 61/58:00:d6:6d:04/06:00:00:00:00/40 tag 0 ncq dma 831488 out
[   59.757324][ T1116]          res 50/00:00:00:00:00/00:00:00:00:00/00 Emask 0x1 (device error)
[   59.764851][ T1116] ata1.00: status: { DRDY }
[   59.766900][ T1116] ata1.00: failed command: WRITE FPDMA QUEUED
[   59.769743][ T1116] ata1.00: cmd 61/c8:f0:0e:69:04/04:00:00:00:00/40 tag 30 ncq dma 626688 out
[   59.769743][ T1116]          res 50/00:00:00:00:00/00:00:00:00:00/00 Emask 0x1 (device error)
[   59.777328][ T1116] ata1.00: status: { DRDY }
[   59.780442][ T1116] ata1.00: configured for UDMA/100
[   59.783246][ T1116] ata1: EH complete
qemu-system-x86_64: ahci: PRDT length for NCQ command (0x0) is smaller than the requested size (0x400000)
qemu-system-x86_64: ahci: PRDT length for NCQ command (0x0) is smaller than the requested size (0x400000)
[   60.002677][ T1116] ata1.00: Read log 0x10 page 0x00 failed, Emask 0x1
[   60.005615][ T1116] ata1: failed to read log page 10h (errno=-5)
[   60.008370][ T1116] ata1.00: NCQ disabled due to excessive errors
[   60.011117][ T1116] ata1.00: exception Emask 0x1 SAct 0x89000000 SErr 0x0 action 0x0
[   60.014746][ T1116] ata1.00: irq_stat 0x41000000
[   60.016900][ T1116] ata1.00: failed command: WRITE FPDMA QUEUED
[   60.019566][ T1116] ata1.00: cmd 61/00:c0:f6:06:05/20:00:00:00:00/40 tag 24 ncq dma 4194304 ou
[   60.019566][ T1116]          res 50/04:00:00:00:00/00:00:00:00:00/00 Emask 0x1 (device error)
[   60.027211][ T1116] ata1.00: status: { DRDY }
[   60.029244][ T1116] ata1.00: error: { ABRT }
[   60.031278][ T1116] ata1.00: failed command: WRITE FPDMA QUEUED
[   60.034084][ T1116] ata1.00: cmd 61/00:d8:36:61:05/20:00:00:00:00/40 tag 27 ncq dma 4194304 ou
[   60.034084][ T1116]          res 50/04:00:00:00:00/00:00:00:00:00/00 Emask 0x1 (device error)
[   60.041564][ T1116] ata1.00: status: { DRDY }
[   60.043728][ T1116] ata1.00: error: { ABRT }
[   60.045740][ T1116] ata1.00: failed command: WRITE FPDMA QUEUED
[   60.048454][ T1116] ata1.00: cmd 61/38:f8:36:81:05/0d:00:00:00:00/40 tag 31 ncq dma 1732608 ou
[   60.048454][ T1116]          res 50/04:00:00:00:00/00:00:00:00:00/00 Emask 0x1 (device error)
[   60.056127][ T1116] ata1.00: status: { DRDY }
[   60.058176][ T1116] ata1.00: error: { ABRT }
[   60.061129][ T1116] ata1.00: configured for UDMA/100
[   60.064028][ T1116] 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-build1140076034=/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/ccLEWSPc.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=1223d552580000