Re: [RESEND][PATCH] ima: Set and clear FMODE_CAN_READ in ima_calc_file_hash()

On Fri, Nov 13, 2020 at 09:01:32AM +0100, Roberto Sassu wrote:

Commit a1f9b1c0439db ("integrity/ima: switch to using __kernel_read") replaced the __vfs_read() call in integrity_kernel_read() with __kernel_read(), a new helper introduced by commit 61a707c543e2a ("fs: add a __kernel_read helper").

Since the new helper requires that also the FMODE_CAN_READ flag is set in file->f_mode, this patch saves the original f_mode and sets the flag if the the file descriptor has the necessary file operation. Lastly, it restores the original f_mode at the end of ima_calc_file_hash().

This looks bogus. FMODE_CAN_READ has a pretty clear definition and you can't just go and read things if it is not set. Also f_mode manipulations on a life file are racy.

Cc: stable@vger.kernel.org # 5.8.x Fixes: a1f9b1c0439db ("integrity/ima: switch to using __kernel_read") Signed-off-by: Roberto Sassu roberto.sassu@huawei.com

---

security/integrity/ima/ima_crypto.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/security/integrity/ima/ima_crypto.c b/security/integrity/ima/ima_crypto.c index 21989fa0c107..22ed86a0c964 100644 --- a/security/integrity/ima/ima_crypto.c +++ b/security/integrity/ima/ima_crypto.c @@ -537,6 +537,7 @@ int ima_calc_file_hash(struct file *file, struct ima_digest_data *hash) loff_t i_size; int rc; struct file *f = file;

• fmode_t saved_mode; bool new_file_instance = false, modified_mode = false;

/* @@ -550,7 +551,7 @@ int ima_calc_file_hash(struct file *file, struct ima_digest_data *hash) } /* Open a new file instance in O_RDONLY if we cannot read */

• if (!(file->f_mode & FMODE_READ)) {

• if (!(file->f_mode & FMODE_READ) || !(file->f_mode & FMODE_CAN_READ)) { int flags = file->f_flags & ~(O_WRONLY | O_APPEND | O_TRUNC | O_CREAT | O_NOCTTY | O_EXCL); flags |= O_RDONLY;

@@ -562,7 +563,10 @@ int ima_calc_file_hash(struct file *file, struct ima_digest_data *hash) */ pr_info_ratelimited("Unable to reopen file for reading.\n"); f = file;

• 	saved_mode = f->f_mode;
  f->f_mode |= FMODE_READ;
  

• 	if (likely(file->f_op->read || file->f_op->read_iter))
  

• 		f->f_mode |= FMODE_CAN_READ;
  modified_mode = true;
  

  } else { new_file_instance = true;

@@ -582,7 +586,7 @@ int ima_calc_file_hash(struct file *file, struct ima_digest_data *hash) if (new_file_instance) fput(f); else if (modified_mode)

• f->f_mode &= ~FMODE_READ;
  

• f->f_mode = saved_mode;
  

  return rc;

} -- 2.27.GIT

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