From: Jaewon Yang Date: Sun, 12 Jul 2026 17:11:47 +0000 (+0900) Subject: tpm: Make the TPM character devices non-seekable X-Git-Tag: v7.2-rc3~1 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=f20d61c22bcaf172d6790b6500e3838e532e71c8;p=thirdparty%2Fkernel%2Flinux.git tpm: Make the TPM character devices non-seekable The TPM character devices expose a sequential command/response interface, but their open handlers leave FMODE_PREAD and FMODE_PWRITE enabled. After a command leaves a response pending, pread(fd, buf, 16, 0x1400) passes 0x1400 as *off to tpm_common_read(). The transfer length is bounded by response_length, but the offset is used unchecked when forming data_buffer + *off. A sufficiently large offset therefore causes an out-of-bounds heap read through copy_to_user() and, if the copy succeeds, an out-of-bounds zero-write through the following memset(). Positional I/O does not provide coherent semantics for this interface. An arbitrary pread offset cannot represent how much of a response has been consumed sequentially. The write callback always stores a command at the start of data_buffer, while pwrite() does not update file->f_pos and can leave the sequential read cursor stale. Call nonseekable_open() from both open handlers. This removes FMODE_PREAD and FMODE_PWRITE, causing positional reads and writes to fail with -ESPIPE before reaching the TPM callbacks, and explicitly marks the files non-seekable. Normal read() and write() continue to use the existing sequential f_pos cursor, leaving the response state machine unchanged. Tested on Linux 6.12 with KASAN and a swtpm TPM2 device: - sequential partial reads returned the complete response - pread() and preadv() with offset 0x1400 returned -ESPIPE - pwrite() and pwritev() with offset zero returned -ESPIPE - the pending response remained intact after the rejected operations - a subsequent normal command/response cycle completed normally - no KASAN report was produced. Fixes: 9488585b21be ("tpm: add support for partial reads") Link: https://lore.kernel.org/all/20260710090217.191289-1-yong010301@gmail.com/ Cc: stable@vger.kernel.org Signed-off-by: Jaewon Yang Signed-off-by: Linus Torvalds --- diff --git a/drivers/char/tpm/tpm-dev.c b/drivers/char/tpm/tpm-dev.c index 2779a8738c59..74488f0a7b78 100644 --- a/drivers/char/tpm/tpm-dev.c +++ b/drivers/char/tpm/tpm-dev.c @@ -36,7 +36,7 @@ static int tpm_open(struct inode *inode, struct file *file) tpm_common_open(file, chip, priv, NULL); - return 0; + return nonseekable_open(inode, file); out: clear_bit(0, &chip->is_open); diff --git a/drivers/char/tpm/tpmrm-dev.c b/drivers/char/tpm/tpmrm-dev.c index f48d4d9e179c..19e8f2779265 100644 --- a/drivers/char/tpm/tpmrm-dev.c +++ b/drivers/char/tpm/tpmrm-dev.c @@ -29,7 +29,7 @@ static int tpmrm_open(struct inode *inode, struct file *file) tpm_common_open(file, chip, &priv->priv, &priv->space); - return 0; + return nonseekable_open(inode, file); } static int tpmrm_release(struct inode *inode, struct file *file)