| Message ID | 20241111065105.82431-1-jinghao7@illinois.edu (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | ipvs: fix UB due to uninitialized stack access in ip_vs_protocol_init() | expand |
Hello, On Mon, 11 Nov 2024, Jinghao Jia wrote: > Under certain kernel configurations when building with Clang/LLVM, the > compiler does not generate a return or jump as the terminator > instruction for ip_vs_protocol_init(), triggering the following objtool > warning during build time: > > vmlinux.o: warning: objtool: ip_vs_protocol_init() falls through to next function __initstub__kmod_ip_vs_rr__935_123_ip_vs_rr_init6() > > At runtime, this either causes an oops when trying to load the ipvs > module or a boot-time panic if ipvs is built-in. This same issue has > been reported by the Intel kernel test robot previously. > > Digging deeper into both LLVM and the kernel code reveals this to be a > undefined behavior problem. ip_vs_protocol_init() uses a on-stack buffer > of 64 chars to store the registered protocol names and leaves it > uninitialized after definition. The function calls strnlen() when > concatenating protocol names into the buffer. With CONFIG_FORTIFY_SOURCE > strnlen() performs an extra step to check whether the last byte of the > input char buffer is a null character (commit 3009f891bb9f ("fortify: > Allow strlen() and strnlen() to pass compile-time known lengths")). > This, together with possibly other configurations, cause the following > IR to be generated: > > define hidden i32 @ip_vs_protocol_init() local_unnamed_addr #5 section ".init.text" align 16 !kcfi_type !29 { > %1 = alloca [64 x i8], align 16 > ... > > 14: ; preds = %11 > %15 = getelementptr inbounds i8, ptr %1, i64 63 > %16 = load i8, ptr %15, align 1 > %17 = tail call i1 @llvm.is.constant.i8(i8 %16) > %18 = icmp eq i8 %16, 0 > %19 = select i1 %17, i1 %18, i1 false > br i1 %19, label %20, label %23 > > 20: ; preds = %14 > %21 = call i64 @strlen(ptr noundef nonnull dereferenceable(1) %1) #23 > ... > > 23: ; preds = %14, %11, %20 > %24 = call i64 @strnlen(ptr noundef nonnull dereferenceable(1) %1, i64 noundef 64) #24 > ... > } > > The above code calculates the address of the last char in the buffer > (value %15) and then loads from it (value %16). Because the buffer is > never initialized, the LLVM GVN pass marks value %16 as undefined: > > %13 = getelementptr inbounds i8, ptr %1, i64 63 > br i1 undef, label %14, label %17 > > This gives later passes (SCCP, in particular) to more DCE opportunities > by propagating the undef value further, and eventually removes > everything after the load on the uninitialized stack location: > > define hidden i32 @ip_vs_protocol_init() local_unnamed_addr #0 section ".init.text" align 16 !kcfi_type !11 { > %1 = alloca [64 x i8], align 16 > ... > > 12: ; preds = %11 > %13 = getelementptr inbounds i8, ptr %1, i64 63 > unreachable > } > > In this way, the generated native code will just fall through to the > next function, as LLVM does not generate any code for the unreachable IR > instruction and leaves the function without a terminator. > > Zero the on-stack buffer to avoid this possible UB. > > Reported-by: kernel test robot <lkp@intel.com> > Closes: https://lore.kernel.org/oe-kbuild-all/202402100205.PWXIz1ZK-lkp@intel.com/ > Co-developed-by: Ruowen Qin <ruqin@redhat.com> > Signed-off-by: Ruowen Qin <ruqin@redhat.com> > Signed-off-by: Jinghao Jia <jinghao7@illinois.edu> Looks good to me, thanks! I assume it is for net-next/nf-next, right? Acked-by: Julian Anastasov <ja@ssi.bg> > --- > net/netfilter/ipvs/ip_vs_proto.c | 4 +--- > 1 file changed, 1 insertion(+), 3 deletions(-) > > diff --git a/net/netfilter/ipvs/ip_vs_proto.c b/net/netfilter/ipvs/ip_vs_proto.c > index f100da4ba3bc..a9fd1d3fc2cb 100644 > --- a/net/netfilter/ipvs/ip_vs_proto.c > +++ b/net/netfilter/ipvs/ip_vs_proto.c > @@ -340,7 +340,7 @@ void __net_exit ip_vs_protocol_net_cleanup(struct netns_ipvs *ipvs) > > int __init ip_vs_protocol_init(void) > { > - char protocols[64]; > + char protocols[64] = { 0 }; > #define REGISTER_PROTOCOL(p) \ > do { \ > register_ip_vs_protocol(p); \ > @@ -348,8 +348,6 @@ int __init ip_vs_protocol_init(void) > strcat(protocols, (p)->name); \ > } while (0) > > - protocols[0] = '\0'; > - protocols[2] = '\0'; > #ifdef CONFIG_IP_VS_PROTO_TCP > REGISTER_PROTOCOL(&ip_vs_protocol_tcp); > #endif > -- > 2.47.0 Regards -- Julian Anastasov <ja@ssi.bg>
Hi Julian, Thanks for getting back to us! On 11/18/24 6:41 AM, Julian Anastasov wrote: > > Hello, > > On Mon, 11 Nov 2024, Jinghao Jia wrote: > >> Under certain kernel configurations when building with Clang/LLVM, the >> compiler does not generate a return or jump as the terminator >> instruction for ip_vs_protocol_init(), triggering the following objtool >> warning during build time: >> >> vmlinux.o: warning: objtool: ip_vs_protocol_init() falls through to next function __initstub__kmod_ip_vs_rr__935_123_ip_vs_rr_init6() >> >> At runtime, this either causes an oops when trying to load the ipvs >> module or a boot-time panic if ipvs is built-in. This same issue has >> been reported by the Intel kernel test robot previously. >> >> Digging deeper into both LLVM and the kernel code reveals this to be a >> undefined behavior problem. ip_vs_protocol_init() uses a on-stack buffer >> of 64 chars to store the registered protocol names and leaves it >> uninitialized after definition. The function calls strnlen() when >> concatenating protocol names into the buffer. With CONFIG_FORTIFY_SOURCE >> strnlen() performs an extra step to check whether the last byte of the >> input char buffer is a null character (commit 3009f891bb9f ("fortify: >> Allow strlen() and strnlen() to pass compile-time known lengths")). >> This, together with possibly other configurations, cause the following >> IR to be generated: >> >> define hidden i32 @ip_vs_protocol_init() local_unnamed_addr #5 section ".init.text" align 16 !kcfi_type !29 { >> %1 = alloca [64 x i8], align 16 >> ... >> >> 14: ; preds = %11 >> %15 = getelementptr inbounds i8, ptr %1, i64 63 >> %16 = load i8, ptr %15, align 1 >> %17 = tail call i1 @llvm.is.constant.i8(i8 %16) >> %18 = icmp eq i8 %16, 0 >> %19 = select i1 %17, i1 %18, i1 false >> br i1 %19, label %20, label %23 >> >> 20: ; preds = %14 >> %21 = call i64 @strlen(ptr noundef nonnull dereferenceable(1) %1) #23 >> ... >> >> 23: ; preds = %14, %11, %20 >> %24 = call i64 @strnlen(ptr noundef nonnull dereferenceable(1) %1, i64 noundef 64) #24 >> ... >> } >> >> The above code calculates the address of the last char in the buffer >> (value %15) and then loads from it (value %16). Because the buffer is >> never initialized, the LLVM GVN pass marks value %16 as undefined: >> >> %13 = getelementptr inbounds i8, ptr %1, i64 63 >> br i1 undef, label %14, label %17 >> >> This gives later passes (SCCP, in particular) to more DCE opportunities One small request: if you could help us remove the extra "to" in the above sentence when committing this patch, it would be great. >> by propagating the undef value further, and eventually removes >> everything after the load on the uninitialized stack location: >> >> define hidden i32 @ip_vs_protocol_init() local_unnamed_addr #0 section ".init.text" align 16 !kcfi_type !11 { >> %1 = alloca [64 x i8], align 16 >> ... >> >> 12: ; preds = %11 >> %13 = getelementptr inbounds i8, ptr %1, i64 63 >> unreachable >> } >> >> In this way, the generated native code will just fall through to the >> next function, as LLVM does not generate any code for the unreachable IR >> instruction and leaves the function without a terminator. >> >> Zero the on-stack buffer to avoid this possible UB. >> >> Reported-by: kernel test robot <lkp@intel.com> >> Closes: https://urldefense.com/v3/__https://lore.kernel.org/oe-kbuild-all/202402100205.PWXIz1ZK-lkp@intel.com/__;!!DZ3fjg!823fsY09q3IcP8uThu-yUuuQaiwQOR7gZJhV9JNWdxzerlkYJ4JkZGYuq4iO1DKqaErCulk1CGir$ >> Co-developed-by: Ruowen Qin <ruqin@redhat.com> >> Signed-off-by: Ruowen Qin <ruqin@redhat.com> >> Signed-off-by: Jinghao Jia <jinghao7@illinois.edu> > > Looks good to me, thanks! I assume it is for > net-next/nf-next, right? I am actually not familiar with the netfilter trees. IMHO this should also be back-ported to the stable kernels -- I wonder if net-next/nf-next is a good tree for this? > > Acked-by: Julian Anastasov <ja@ssi.bg> > >> --- >> net/netfilter/ipvs/ip_vs_proto.c | 4 +--- >> 1 file changed, 1 insertion(+), 3 deletions(-) >> >> diff --git a/net/netfilter/ipvs/ip_vs_proto.c b/net/netfilter/ipvs/ip_vs_proto.c >> index f100da4ba3bc..a9fd1d3fc2cb 100644 >> --- a/net/netfilter/ipvs/ip_vs_proto.c >> +++ b/net/netfilter/ipvs/ip_vs_proto.c >> @@ -340,7 +340,7 @@ void __net_exit ip_vs_protocol_net_cleanup(struct netns_ipvs *ipvs) >> >> int __init ip_vs_protocol_init(void) >> { >> - char protocols[64]; >> + char protocols[64] = { 0 }; >> #define REGISTER_PROTOCOL(p) \ >> do { \ >> register_ip_vs_protocol(p); \ >> @@ -348,8 +348,6 @@ int __init ip_vs_protocol_init(void) >> strcat(protocols, (p)->name); \ >> } while (0) >> >> - protocols[0] = '\0'; >> - protocols[2] = '\0'; >> #ifdef CONFIG_IP_VS_PROTO_TCP >> REGISTER_PROTOCOL(&ip_vs_protocol_tcp); >> #endif >> -- >> 2.47.0 > > Regards > > -- > Julian Anastasov <ja@ssi.bg> > Best, Jinghao
Hello, On Tue, 19 Nov 2024, Jinghao Jia wrote: > On 11/18/24 6:41 AM, Julian Anastasov wrote: > > > > On Mon, 11 Nov 2024, Jinghao Jia wrote: > > > >> Under certain kernel configurations when building with Clang/LLVM, the > >> compiler does not generate a return or jump as the terminator > >> instruction for ip_vs_protocol_init(), triggering the following objtool > >> warning during build time: > >> > >> vmlinux.o: warning: objtool: ip_vs_protocol_init() falls through to next function __initstub__kmod_ip_vs_rr__935_123_ip_vs_rr_init6() > >> ... > >> This gives later passes (SCCP, in particular) to more DCE opportunities > > One small request: if you could help us remove the extra "to" in the above > sentence when committing this patch, it would be great. > ... > > Looks good to me, thanks! I assume it is for > > net-next/nf-next, right? > > I am actually not familiar with the netfilter trees. IMHO this should also be > back-ported to the stable kernels -- I wonder if net-next/nf-next is a good > tree for this? Then may be it is better to send [PATCHv2 net] after fixing the above "to" and selecting proper commit for a Fixes line (probably the initial commit 1da177e4c3f4 ?). > >> - char protocols[64]; > >> + char protocols[64] = { 0 }; > >> #define REGISTER_PROTOCOL(p) \ > >> do { \ > >> register_ip_vs_protocol(p); \ > >> @@ -348,8 +348,6 @@ int __init ip_vs_protocol_init(void) > >> strcat(protocols, (p)->name); \ > >> } while (0) > >> > >> - protocols[0] = '\0'; > >> - protocols[2] = '\0'; > >> #ifdef CONFIG_IP_VS_PROTO_TCP > >> REGISTER_PROTOCOL(&ip_vs_protocol_tcp); > >> #endif Regards -- Julian Anastasov <ja@ssi.bg>
diff --git a/net/netfilter/ipvs/ip_vs_proto.c b/net/netfilter/ipvs/ip_vs_proto.c index f100da4ba3bc..a9fd1d3fc2cb 100644 --- a/net/netfilter/ipvs/ip_vs_proto.c +++ b/net/netfilter/ipvs/ip_vs_proto.c @@ -340,7 +340,7 @@ void __net_exit ip_vs_protocol_net_cleanup(struct netns_ipvs *ipvs) int __init ip_vs_protocol_init(void) { - char protocols[64]; + char protocols[64] = { 0 }; #define REGISTER_PROTOCOL(p) \ do { \ register_ip_vs_protocol(p); \ @@ -348,8 +348,6 @@ int __init ip_vs_protocol_init(void) strcat(protocols, (p)->name); \ } while (0) - protocols[0] = '\0'; - protocols[2] = '\0'; #ifdef CONFIG_IP_VS_PROTO_TCP REGISTER_PROTOCOL(&ip_vs_protocol_tcp); #endif
Under certain kernel configurations when building with Clang/LLVM, the compiler does not generate a return or jump as the terminator instruction for ip_vs_protocol_init(), triggering the following objtool warning during build time: vmlinux.o: warning: objtool: ip_vs_protocol_init() falls through to next function __initstub__kmod_ip_vs_rr__935_123_ip_vs_rr_init6() At runtime, this either causes an oops when trying to load the ipvs module or a boot-time panic if ipvs is built-in. This same issue has been reported by the Intel kernel test robot previously. Digging deeper into both LLVM and the kernel code reveals this to be a undefined behavior problem. ip_vs_protocol_init() uses a on-stack buffer of 64 chars to store the registered protocol names and leaves it uninitialized after definition. The function calls strnlen() when concatenating protocol names into the buffer. With CONFIG_FORTIFY_SOURCE strnlen() performs an extra step to check whether the last byte of the input char buffer is a null character (commit 3009f891bb9f ("fortify: Allow strlen() and strnlen() to pass compile-time known lengths")). This, together with possibly other configurations, cause the following IR to be generated: define hidden i32 @ip_vs_protocol_init() local_unnamed_addr #5 section ".init.text" align 16 !kcfi_type !29 { %1 = alloca [64 x i8], align 16 ... 14: ; preds = %11 %15 = getelementptr inbounds i8, ptr %1, i64 63 %16 = load i8, ptr %15, align 1 %17 = tail call i1 @llvm.is.constant.i8(i8 %16) %18 = icmp eq i8 %16, 0 %19 = select i1 %17, i1 %18, i1 false br i1 %19, label %20, label %23 20: ; preds = %14 %21 = call i64 @strlen(ptr noundef nonnull dereferenceable(1) %1) #23 ... 23: ; preds = %14, %11, %20 %24 = call i64 @strnlen(ptr noundef nonnull dereferenceable(1) %1, i64 noundef 64) #24 ... } The above code calculates the address of the last char in the buffer (value %15) and then loads from it (value %16). Because the buffer is never initialized, the LLVM GVN pass marks value %16 as undefined: %13 = getelementptr inbounds i8, ptr %1, i64 63 br i1 undef, label %14, label %17 This gives later passes (SCCP, in particular) to more DCE opportunities by propagating the undef value further, and eventually removes everything after the load on the uninitialized stack location: define hidden i32 @ip_vs_protocol_init() local_unnamed_addr #0 section ".init.text" align 16 !kcfi_type !11 { %1 = alloca [64 x i8], align 16 ... 12: ; preds = %11 %13 = getelementptr inbounds i8, ptr %1, i64 63 unreachable } In this way, the generated native code will just fall through to the next function, as LLVM does not generate any code for the unreachable IR instruction and leaves the function without a terminator. Zero the on-stack buffer to avoid this possible UB. Reported-by: kernel test robot <lkp@intel.com> Closes: https://lore.kernel.org/oe-kbuild-all/202402100205.PWXIz1ZK-lkp@intel.com/ Co-developed-by: Ruowen Qin <ruqin@redhat.com> Signed-off-by: Ruowen Qin <ruqin@redhat.com> Signed-off-by: Jinghao Jia <jinghao7@illinois.edu> --- net/netfilter/ipvs/ip_vs_proto.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-)