On Mon, Feb 17, 2025 at 6:50 PM Eric Biggers <ebiggers@kernel.org> wrote:

On Mon, Feb 17, 2025 at 06:43:15PM +0000, Lucas Tanure wrote:

...

Hi,

I am working with Android 13 and V5.15 kernel. During our development, I found a memory leak using kmemleak.

Steps I did to find the memleak: mount -t debugfs debugfs /sys/kernel/debug echo scan=5 > /sys/kernel/debug/kmemleak cat /sys/kernel/debug/kmemleak

Stack I got (hundreds of them): unreferenced object 0xffffff8101d31000 (size 1024): comm "binder:1357_2", pid 1357, jiffies 4294899464 (age 394.468s) hex dump (first 32 bytes): 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ backtrace: [<ffffffd327cac060>] crypto_create_tfm_node+0x64/0x228 [<ffffffd3279f8c4c>] fscrypt_prepare_key+0xbc/0x230 [<ffffffd3279f9758>] fscrypt_setup_v1_file_key+0x48c/0x510 [<ffffffd3279f8394>] fscrypt_setup_encryption_info+0x210/0x43c [<ffffffd3279f8108>] fscrypt_prepare_new_inode+0x128/0x1a4 [<ffffffd327bcc878>] f2fs_new_inode+0x27c/0x89c [<ffffffd327bce7c4>] f2fs_mkdir+0x78/0x278 [<ffffffd32796a3bc>] vfs_mkdir+0x138/0x204 [<ffffffd32796a108>] do_mkdirat+0x88/0x204 [<ffffffd32796a068>] __arm64_sys_mkdirat+0x40/0x58 [<ffffffd3274be5d4>] invoke_syscall+0x60/0x150 [<ffffffd3274be528>] el0_svc_common+0xc8/0x114 [<ffffffd3274be3f0>] do_el0_svc+0x28/0x98 [<ffffffd328abcf88>] el0_svc+0x28/0x90 [<ffffffd328abcefc>] el0t_64_sync_handler+0x88/0xec [<ffffffd32741164c>] el0t_64_sync+0x1b8/0x1bc

After checking upstream, I came up with the following: cff805b1518f fscrypt: fix keyring memory leak on mount failure

But my kernel has this patch. So I continued to dig around this and saw the function fscrypt_prepare_key in fs/crypto/keysetup.c for V5.15. I can't see the pointer tfm being used anywhere or saved, and smp_store_release doesn't kfree it. Is smp_store_release doing something with that pointer that makes this memory leak a false positive?

Any help with this issue would be much appreciated. Thanks

The pointer to the crypto_skcipher 'tfm' is stored in the fscrypt_inode_info (previously fscrypt_info) which is stored in inode::i_crypt_info. It gets freed when the inode is evicted. I don't know why you're getting a kmemleak warning. Perhaps f2fs in that version of the kernel has a bug that is leaking inodes.

Thanks. How do you check for leaking inodes? Do you have any start point (function) to look at?

smp_store_release is just a fancy way of doing a store that includes a memory barrier.

- Eric

Lucas