From: Christoph Hellwig [mailto:hch@infradead.org] Sent: Saturday, November 14, 2020 12:11 PM 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.
FMODE_CAN_READ was not set because f_mode does not have FMODE_READ. In the patch, I check if the former can be set similarly to the way it is done in file_table.c and open.c.
Is there a better way to read a file when the file was not opened for reading and a new file descriptor cannot be created?
Thanks
Roberto
HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063 Managing Director: Li Peng, Li Jian, Shi Yanli
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 forreading.\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;@@ -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;}
-- 2.27.GIT
---end quoted text---