[PATCH] selinux: avoid 64-bit division of inode numbers

[PATCH] selinux: avoid 64-bit division of inode numbers

[Paul Moore]

As reported by Arnd, a previous change to convert the selinuxfs inode
numbers to u64 to match the rest of the kernel caused a problem on 32-bit
systems:

  arm-linux-gnueabi-ld: .../selinuxfs.o: in function `sel_read_class':
   selinuxfs.c:(.text+0xdcc): undefined reference to `__aeabi_uldivmod'
  arm-linux-gnueabi-ld: .../selinuxfs.o: in function `sel_read_perm':
   selinuxfs.c:(.text+0xed0): undefined reference to `__aeabi_uldivmod'

Since we don't currently use more than 24-bits in the selinuxfs inodes
(see SEL_INO_MASK), fix this by applying the SEL_INO_MASK to the
selinuxfs inode numbers and casting to a u32 before performing any
division operations.

Fixes: fc68b6a45f16 ("selinux: convert selinuxfs inode numbers from unsigned long to u64")
Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Paul Moore <paul@paul-moore.com>
---
 security/selinux/selinuxfs.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
index 292302eb60f3..d864c314c873 100644
--- a/security/selinux/selinuxfs.c
+++ b/security/selinux/selinuxfs.c
@@ -1574,7 +1574,8 @@ static inline u64 sel_class_to_ino(u16 class)
 
 static inline u16 sel_ino_to_class(u64 ino)
 {
-	return (ino & SEL_INO_MASK) / (SEL_VEC_MAX + 1);
+	u32 ino_masked = ino & SEL_INO_MASK;
+	return ino_masked / (SEL_VEC_MAX + 1);
 }
 
 static inline u64 sel_perm_to_ino(u16 class, u32 perm)
@@ -1584,7 +1585,8 @@ static inline u64 sel_perm_to_ino(u16 class, u32 perm)
 
 static inline u32 sel_ino_to_perm(u64 ino)
 {
-	return (ino & SEL_INO_MASK) % (SEL_VEC_MAX + 1);
+	u32 ino_masked = ino & SEL_INO_MASK;
+	return ino_masked % (SEL_VEC_MAX + 1);
 }
 
 static ssize_t sel_read_class(struct file *file, char __user *buf,
-- 
2.55.0

Re: [PATCH] selinux: avoid 64-bit division of inode numbers

[sashiko-bot]

> As reported by Arnd, a previous change to convert the selinuxfs inode
> numbers to u64 to match the rest of the kernel caused a problem on 32-bit
> systems:
> 
>   arm-linux-gnueabi-ld: .../selinuxfs.o: in function `sel_read_class':
>    selinuxfs.c:(.text+0xdcc): undefined reference to `__aeabi_uldivmod'
>   arm-linux-gnueabi-ld: .../selinuxfs.o: in function `sel_read_perm':
>    selinuxfs.c:(.text+0xed0): undefined reference to `__aeabi_uldivmod'
> 
> Since we don't currently use more than 24-bits in the selinuxfs inodes
> (see SEL_INO_MASK), fix this by applying the SEL_INO_MASK to the
> selinuxfs inode numbers and casting to a u32 before performing any
> division operations.
> 
> Fixes: fc68b6a45f16 ("selinux: convert selinuxfs inode numbers from unsigned long to u64")
> Reported-by: Arnd Bergmann <arnd@arndb.de>
> Signed-off-by: Paul Moore <paul@paul-moore.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260915213807.481355-2-paul@paul-moore.com?part=1

Re: [PATCH] selinux: avoid 64-bit division of inode numbers

[Paul Moore]

On Tue, Sep 15, 2026 at 5:38 PM Paul Moore <paul@paul-moore.com> wrote:
>
> As reported by Arnd, a previous change to convert the selinuxfs inode
> numbers to u64 to match the rest of the kernel caused a problem on 32-bit
> systems:
>
>   arm-linux-gnueabi-ld: .../selinuxfs.o: in function `sel_read_class':
>    selinuxfs.c:(.text+0xdcc): undefined reference to `__aeabi_uldivmod'
>   arm-linux-gnueabi-ld: .../selinuxfs.o: in function `sel_read_perm':
>    selinuxfs.c:(.text+0xed0): undefined reference to `__aeabi_uldivmod'
>
> Since we don't currently use more than 24-bits in the selinuxfs inodes
> (see SEL_INO_MASK), fix this by applying the SEL_INO_MASK to the
> selinuxfs inode numbers and casting to a u32 before performing any
> division operations.
>
> Fixes: fc68b6a45f16 ("selinux: convert selinuxfs inode numbers from unsigned long to u64")
> Reported-by: Arnd Bergmann <arnd@arndb.de>
> Signed-off-by: Paul Moore <paul@paul-moore.com>
> ---
>  security/selinux/selinuxfs.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)

Merged into selinux/dev.

-- 
paul-moore.com