> From: Christoph Hellwig [mailto:hch@xxxxxxxxxxxxx] > 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@xxxxxxxxxxxxxxx # 5.8.x > > Fixes: a1f9b1c0439db ("integrity/ima: switch to using __kernel_read") > > Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx> > > --- > > 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 > > > ---end quoted text---
