* Re: [PATCH bpf-next] bpf: reject BPF_MAP_TYPE_INODE_STORAGE creation if BPF LSM is uninitialized
2026-06-28 20:11 [PATCH bpf-next] bpf: reject BPF_MAP_TYPE_INODE_STORAGE creation if BPF LSM is uninitialized Matt Bobrowski
@ 2026-06-29 5:25 ` Emil Tsalapatis
2026-06-29 6:30 ` Amery Hung
2026-06-30 15:31 ` Daniel Borkmann
2 siblings, 0 replies; 5+ messages in thread
From: Emil Tsalapatis @ 2026-06-29 5:25 UTC (permalink / raw)
To: Matt Bobrowski, bpf
Cc: Alexei Starovoitov, Daniel Borkmann, Paul Moore, Andrii Nakryiko,
Martin KaFai Lau, Eduard Zingerman, Song Liu, Yonghong Song,
Jiri Olsa, oxsignal
On Sun Jun 28, 2026 at 4:11 PM EDT, Matt Bobrowski wrote:
> When CONFIG_BPF_LSM=y is set, BPF inode storage maps
> (BPF_MAP_TYPE_INODE_STORAGE) are compiled into the kernel. However,
> if the BPF LSM is not explicitly enabled at boot time (e.g. omitted
> from the "lsm=" boot parameter), lsm_prepare() is never executed for
> the BPF LSM.
>
> Consequently, the BPF inode security blob offset
> (bpf_lsm_blob_sizes.lbs_inode) is never initialized and remains at its
> default compiled size of 8 bytes instead of being updated to a valid
> offset past the reserved struct rcu_head (typically 16 bytes or more).
>
> When a privileged user creates and updates a
> BPF_MAP_TYPE_INODE_STORAGE map, bpf_inode() evaluates
> inode->i_security + 8. This erroneously aliases the struct
> rcu_head.func callback pointer at the beginning of the
> inode->i_security blob. During subsequent map element cleanup or inode
> destruction, writing NULL to owner_storage clears the queued RCU
> callback pointer. When rcu_do_batch() later executes the queued
> callback, it attempts an instruction fetch at address 0x0, triggering
> an immediate kernel panic.
>
> Fix this by introducing a global bpf_lsm_initialized boolean flag
> marked with __ro_after_init. Set this flag to true inside
> bpf_lsm_init() when the LSM framework successfully registers the BPF
> LSM. Gate map allocation in inode_storage_map_alloc() on this flag,
> returning -EOPNOTSUPP if the BPF LSM is in turn uninitialized.
>
> This fail-fast approach prevents userspace from allocating inode
> storage maps when the supporting BPF LSM infrastructure is absent,
> avoiding zombie map states.
>
> Fixes: 8ea636848aca ("bpf: Implement bpf_local_storage for inodes")
> Reported-by: oxsignal <awo@kakao.com>
> Signed-off-by: Matt Bobrowski <mattbobrowski@google.com>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
It makes sense for since the only users of inode-local storage are
related to LSM (case in point, this whole bug is due to storing the
storage map in the inode's ->security in the first place).
> ---
> include/linux/bpf_lsm.h | 4 ++++
> kernel/bpf/bpf_inode_storage.c | 9 +++++++++
> security/bpf/hooks.c | 3 +++
> 3 files changed, 16 insertions(+)
>
> diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h
> index 143775a27a2a..dda272d78f01 100644
> --- a/include/linux/bpf_lsm.h
> +++ b/include/linux/bpf_lsm.h
> @@ -14,6 +14,8 @@
>
> #ifdef CONFIG_BPF_LSM
>
> +extern bool bpf_lsm_initialized __ro_after_init;
> +
> #define LSM_HOOK(RET, DEFAULT, NAME, ...) \
> RET bpf_lsm_##NAME(__VA_ARGS__);
> #include <linux/lsm_hook_defs.h>
> @@ -56,6 +58,8 @@ bool bpf_lsm_hook_returns_errno(u32 btf_id);
>
> #else /* !CONFIG_BPF_LSM */
>
> +#define bpf_lsm_initialized false
> +
> static inline bool bpf_lsm_is_sleepable_hook(u32 btf_id)
> {
> return false;
> diff --git a/kernel/bpf/bpf_inode_storage.c b/kernel/bpf/bpf_inode_storage.c
> index 0da8d923e39d..f9e81060c1f4 100644
> --- a/kernel/bpf/bpf_inode_storage.c
> +++ b/kernel/bpf/bpf_inode_storage.c
> @@ -178,6 +178,15 @@ static int notsupp_get_next_key(struct bpf_map *map, void *key,
>
> static struct bpf_map *inode_storage_map_alloc(union bpf_attr *attr)
> {
> + /*
> + * Do not allow allocation of BPF_MAP_TYPE_INODE_STORAGE if the BPF LSM
> + * was not initialized by the LSM framework at boot. Without proper
> + * initialization, the BPF inode security blob offset remains unprepared,
> + * causing bpf_inode() to calculate an invalid memory offset and corrupt
> + * inode->i_security.
> + */
> + if (!bpf_lsm_initialized)
> + return ERR_PTR(-EOPNOTSUPP);
> return bpf_local_storage_map_alloc(attr, &inode_cache);
> }
>
> diff --git a/security/bpf/hooks.c b/security/bpf/hooks.c
> index 40efde233f3a..7b98f5d1e2be 100644
> --- a/security/bpf/hooks.c
> +++ b/security/bpf/hooks.c
> @@ -7,6 +7,8 @@
> #include <linux/bpf_lsm.h>
> #include <uapi/linux/lsm.h>
>
> +bool bpf_lsm_initialized __ro_after_init;
> +
> static struct security_hook_list bpf_lsm_hooks[] __ro_after_init = {
> #define LSM_HOOK(RET, DEFAULT, NAME, ...) \
> LSM_HOOK_INIT(NAME, bpf_lsm_##NAME),
> @@ -24,6 +26,7 @@ static int __init bpf_lsm_init(void)
> {
> security_add_hooks(bpf_lsm_hooks, ARRAY_SIZE(bpf_lsm_hooks),
> &bpf_lsmid);
> + bpf_lsm_initialized = true;
> pr_info("LSM support for eBPF active\n");
> return 0;
> }
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH bpf-next] bpf: reject BPF_MAP_TYPE_INODE_STORAGE creation if BPF LSM is uninitialized
2026-06-28 20:11 [PATCH bpf-next] bpf: reject BPF_MAP_TYPE_INODE_STORAGE creation if BPF LSM is uninitialized Matt Bobrowski
2026-06-29 5:25 ` Emil Tsalapatis
@ 2026-06-29 6:30 ` Amery Hung
2026-06-30 15:31 ` Daniel Borkmann
2 siblings, 0 replies; 5+ messages in thread
From: Amery Hung @ 2026-06-29 6:30 UTC (permalink / raw)
To: Matt Bobrowski
Cc: bpf, Alexei Starovoitov, Daniel Borkmann, Paul Moore,
Andrii Nakryiko, Martin KaFai Lau, Eduard Zingerman, Song Liu,
Yonghong Song, Jiri Olsa, oxsignal
On Sun, Jun 28, 2026 at 1:11 PM Matt Bobrowski <mattbobrowski@google.com> wrote:
>
> When CONFIG_BPF_LSM=y is set, BPF inode storage maps
> (BPF_MAP_TYPE_INODE_STORAGE) are compiled into the kernel. However,
> if the BPF LSM is not explicitly enabled at boot time (e.g. omitted
> from the "lsm=" boot parameter), lsm_prepare() is never executed for
> the BPF LSM.
>
> Consequently, the BPF inode security blob offset
> (bpf_lsm_blob_sizes.lbs_inode) is never initialized and remains at its
> default compiled size of 8 bytes instead of being updated to a valid
> offset past the reserved struct rcu_head (typically 16 bytes or more).
>
> When a privileged user creates and updates a
> BPF_MAP_TYPE_INODE_STORAGE map, bpf_inode() evaluates
> inode->i_security + 8. This erroneously aliases the struct
> rcu_head.func callback pointer at the beginning of the
> inode->i_security blob. During subsequent map element cleanup or inode
> destruction, writing NULL to owner_storage clears the queued RCU
> callback pointer. When rcu_do_batch() later executes the queued
> callback, it attempts an instruction fetch at address 0x0, triggering
> an immediate kernel panic.
>
> Fix this by introducing a global bpf_lsm_initialized boolean flag
> marked with __ro_after_init. Set this flag to true inside
> bpf_lsm_init() when the LSM framework successfully registers the BPF
> LSM. Gate map allocation in inode_storage_map_alloc() on this flag,
> returning -EOPNOTSUPP if the BPF LSM is in turn uninitialized.
>
> This fail-fast approach prevents userspace from allocating inode
> storage maps when the supporting BPF LSM infrastructure is absent,
> avoiding zombie map states.
>
> Fixes: 8ea636848aca ("bpf: Implement bpf_local_storage for inodes")
> Reported-by: oxsignal <awo@kakao.com>
> Signed-off-by: Matt Bobrowski <mattbobrowski@google.com>
Reviewed-by: Amery Hung <ameryhung@gmail.com>
> ---
> include/linux/bpf_lsm.h | 4 ++++
> kernel/bpf/bpf_inode_storage.c | 9 +++++++++
> security/bpf/hooks.c | 3 +++
> 3 files changed, 16 insertions(+)
>
> diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h
> index 143775a27a2a..dda272d78f01 100644
> --- a/include/linux/bpf_lsm.h
> +++ b/include/linux/bpf_lsm.h
> @@ -14,6 +14,8 @@
>
> #ifdef CONFIG_BPF_LSM
>
> +extern bool bpf_lsm_initialized __ro_after_init;
> +
> #define LSM_HOOK(RET, DEFAULT, NAME, ...) \
> RET bpf_lsm_##NAME(__VA_ARGS__);
> #include <linux/lsm_hook_defs.h>
> @@ -56,6 +58,8 @@ bool bpf_lsm_hook_returns_errno(u32 btf_id);
>
> #else /* !CONFIG_BPF_LSM */
>
> +#define bpf_lsm_initialized false
> +
> static inline bool bpf_lsm_is_sleepable_hook(u32 btf_id)
> {
> return false;
> diff --git a/kernel/bpf/bpf_inode_storage.c b/kernel/bpf/bpf_inode_storage.c
> index 0da8d923e39d..f9e81060c1f4 100644
> --- a/kernel/bpf/bpf_inode_storage.c
> +++ b/kernel/bpf/bpf_inode_storage.c
> @@ -178,6 +178,15 @@ static int notsupp_get_next_key(struct bpf_map *map, void *key,
>
> static struct bpf_map *inode_storage_map_alloc(union bpf_attr *attr)
> {
> + /*
> + * Do not allow allocation of BPF_MAP_TYPE_INODE_STORAGE if the BPF LSM
> + * was not initialized by the LSM framework at boot. Without proper
> + * initialization, the BPF inode security blob offset remains unprepared,
> + * causing bpf_inode() to calculate an invalid memory offset and corrupt
> + * inode->i_security.
> + */
> + if (!bpf_lsm_initialized)
> + return ERR_PTR(-EOPNOTSUPP);
> return bpf_local_storage_map_alloc(attr, &inode_cache);
> }
>
> diff --git a/security/bpf/hooks.c b/security/bpf/hooks.c
> index 40efde233f3a..7b98f5d1e2be 100644
> --- a/security/bpf/hooks.c
> +++ b/security/bpf/hooks.c
> @@ -7,6 +7,8 @@
> #include <linux/bpf_lsm.h>
> #include <uapi/linux/lsm.h>
>
> +bool bpf_lsm_initialized __ro_after_init;
> +
> static struct security_hook_list bpf_lsm_hooks[] __ro_after_init = {
> #define LSM_HOOK(RET, DEFAULT, NAME, ...) \
> LSM_HOOK_INIT(NAME, bpf_lsm_##NAME),
> @@ -24,6 +26,7 @@ static int __init bpf_lsm_init(void)
> {
> security_add_hooks(bpf_lsm_hooks, ARRAY_SIZE(bpf_lsm_hooks),
> &bpf_lsmid);
> + bpf_lsm_initialized = true;
> pr_info("LSM support for eBPF active\n");
> return 0;
> }
> --
> 2.55.0.rc0.799.gd6f94ed593-goog
>
>
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH bpf-next] bpf: reject BPF_MAP_TYPE_INODE_STORAGE creation if BPF LSM is uninitialized
2026-06-28 20:11 [PATCH bpf-next] bpf: reject BPF_MAP_TYPE_INODE_STORAGE creation if BPF LSM is uninitialized Matt Bobrowski
2026-06-29 5:25 ` Emil Tsalapatis
2026-06-29 6:30 ` Amery Hung
@ 2026-06-30 15:31 ` Daniel Borkmann
2026-07-02 20:55 ` Matt Bobrowski
2 siblings, 1 reply; 5+ messages in thread
From: Daniel Borkmann @ 2026-06-30 15:31 UTC (permalink / raw)
To: Matt Bobrowski, bpf
Cc: Alexei Starovoitov, Paul Moore, Andrii Nakryiko, Martin KaFai Lau,
Eduard Zingerman, Song Liu, Yonghong Song, Jiri Olsa, oxsignal
On 6/28/26 10:11 PM, Matt Bobrowski wrote:
> When CONFIG_BPF_LSM=y is set, BPF inode storage maps
> (BPF_MAP_TYPE_INODE_STORAGE) are compiled into the kernel. However,
> if the BPF LSM is not explicitly enabled at boot time (e.g. omitted
> from the "lsm=" boot parameter), lsm_prepare() is never executed for
> the BPF LSM.
>
> Consequently, the BPF inode security blob offset
> (bpf_lsm_blob_sizes.lbs_inode) is never initialized and remains at its
> default compiled size of 8 bytes instead of being updated to a valid
> offset past the reserved struct rcu_head (typically 16 bytes or more).
>
> When a privileged user creates and updates a
> BPF_MAP_TYPE_INODE_STORAGE map, bpf_inode() evaluates
> inode->i_security + 8. This erroneously aliases the struct
> rcu_head.func callback pointer at the beginning of the
> inode->i_security blob. During subsequent map element cleanup or inode
> destruction, writing NULL to owner_storage clears the queued RCU
> callback pointer. When rcu_do_batch() later executes the queued
> callback, it attempts an instruction fetch at address 0x0, triggering
> an immediate kernel panic.
>
> Fix this by introducing a global bpf_lsm_initialized boolean flag
> marked with __ro_after_init. Set this flag to true inside
> bpf_lsm_init() when the LSM framework successfully registers the BPF
> LSM. Gate map allocation in inode_storage_map_alloc() on this flag,
> returning -EOPNOTSUPP if the BPF LSM is in turn uninitialized.
>
> This fail-fast approach prevents userspace from allocating inode
> storage maps when the supporting BPF LSM infrastructure is absent,
> avoiding zombie map states.
>
> Fixes: 8ea636848aca ("bpf: Implement bpf_local_storage for inodes")
> Reported-by: oxsignal <awo@kakao.com>
> Signed-off-by: Matt Bobrowski <mattbobrowski@google.com>
(Looks like pwbot is asleep; applied to bpf.)
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH bpf-next] bpf: reject BPF_MAP_TYPE_INODE_STORAGE creation if BPF LSM is uninitialized
2026-06-30 15:31 ` Daniel Borkmann
@ 2026-07-02 20:55 ` Matt Bobrowski
0 siblings, 0 replies; 5+ messages in thread
From: Matt Bobrowski @ 2026-07-02 20:55 UTC (permalink / raw)
To: Daniel Borkmann
Cc: bpf, Alexei Starovoitov, Paul Moore, Andrii Nakryiko,
Martin KaFai Lau, Eduard Zingerman, Song Liu, Yonghong Song,
Jiri Olsa, oxsignal
On Tue, Jun 30, 2026 at 05:31:13PM +0200, Daniel Borkmann wrote:
> On 6/28/26 10:11 PM, Matt Bobrowski wrote:
> > When CONFIG_BPF_LSM=y is set, BPF inode storage maps
> > (BPF_MAP_TYPE_INODE_STORAGE) are compiled into the kernel. However,
> > if the BPF LSM is not explicitly enabled at boot time (e.g. omitted
> > from the "lsm=" boot parameter), lsm_prepare() is never executed for
> > the BPF LSM.
> >
> > Consequently, the BPF inode security blob offset
> > (bpf_lsm_blob_sizes.lbs_inode) is never initialized and remains at its
> > default compiled size of 8 bytes instead of being updated to a valid
> > offset past the reserved struct rcu_head (typically 16 bytes or more).
> >
> > When a privileged user creates and updates a
> > BPF_MAP_TYPE_INODE_STORAGE map, bpf_inode() evaluates
> > inode->i_security + 8. This erroneously aliases the struct
> > rcu_head.func callback pointer at the beginning of the
> > inode->i_security blob. During subsequent map element cleanup or inode
> > destruction, writing NULL to owner_storage clears the queued RCU
> > callback pointer. When rcu_do_batch() later executes the queued
> > callback, it attempts an instruction fetch at address 0x0, triggering
> > an immediate kernel panic.
> >
> > Fix this by introducing a global bpf_lsm_initialized boolean flag
> > marked with __ro_after_init. Set this flag to true inside
> > bpf_lsm_init() when the LSM framework successfully registers the BPF
> > LSM. Gate map allocation in inode_storage_map_alloc() on this flag,
> > returning -EOPNOTSUPP if the BPF LSM is in turn uninitialized.
> >
> > This fail-fast approach prevents userspace from allocating inode
> > storage maps when the supporting BPF LSM infrastructure is absent,
> > avoiding zombie map states.
> >
> > Fixes: 8ea636848aca ("bpf: Implement bpf_local_storage for inodes")
> > Reported-by: oxsignal <awo@kakao.com>
> > Signed-off-by: Matt Bobrowski <mattbobrowski@google.com>
>
> (Looks like pwbot is asleep; applied to bpf.)
Thank you Daniel!
^ permalink raw reply [flat|nested] 5+ messages in thread