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Commit f41ced8f108cc80f16509b907cd7ac93944459bc

Authored by Laurent Pinchart
Committed by Linus Torvalds
1 parent bdbeed75b2
Exists in master and in 7 other branches imx_3.0.35_4.1.0, imx_3.10.17_1.0.1_ga, imx_3.10.53_1.1.0_ga, imx_3.14.28_1.0.0_ga, smarc-imx_3.10.53_1.1.0_ga, smarc-imx_3.14.28_1.0.0_ga, smarc-l5.0.0_1.0.0-ga

Check fops_get() return value 

Several subsystem open handlers dereference the fops_get() return value
without checking it for nullness.  This opens a race condition between the
open handler and module unloading.

A module can be marked as being unloaded (MODULE_STATE_GOING) before its
exit function is called and gets the chance to unregister the driver.
During that window open handlers can still be called, and fops_get() will
fail in try_module_get() and return a NULL pointer.

This change checks the fops_get() return value and returns -ENODEV if NULL.

Reported-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk>
Signed-off-by: Laurent Pinchart <laurent.pinchart@skynet.be>
Acked-by: Takashi Iwai <tiwai@suse.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Dave Airlie <airlied@linux.ie>
Acked-by: Mauro Carvalho Chehab <mchehab@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Showing 3 changed files with 13 additions and 0 deletions Side-by-side Diff

drivers/gpu/drm/drm_fops.c
Diff comments   View file @ f41ced8
... ... @@ -183,6 +183,10 @@
183 183  
184 184 old_fops = filp->f_op;
185 185 filp->f_op = fops_get(&dev->driver->fops);
  186 + if (filp->f_op == NULL) {
  187 + filp->f_op = old_fops;
  188 + goto out;
  189 + }
186 190 if (filp->f_op->open && (err = filp->f_op->open(inode, filp))) {
187 191 fops_put(filp->f_op);
188 192 filp->f_op = fops_get(old_fops);
drivers/media/dvb/dvb-core/dvbdev.c
Diff comments   View file @ f41ced8
... ... @@ -79,6 +79,10 @@
79 79 file->private_data = dvbdev;
80 80 old_fops = file->f_op;
81 81 file->f_op = fops_get(dvbdev->fops);
  82 + if (file->f_op == NULL) {
  83 + file->f_op = old_fops;
  84 + goto fail;
  85 + }
82 86 if(file->f_op->open)
83 87 err = file->f_op->open(inode,file);
84 88 if (err) {
... ... @@ -90,6 +94,7 @@
90 94 unlock_kernel();
91 95 return err;
92 96 }
  97 +fail:
93 98 up_read(&minor_rwsem);
94 99 unlock_kernel();
95 100 return -ENODEV;
... ... @@ -152,6 +152,10 @@
152 152 }
153 153 old_fops = file->f_op;
154 154 file->f_op = fops_get(mptr->f_ops);
  155 + if (file->f_op == NULL) {
  156 + file->f_op = old_fops;
  157 + return -ENODEV;
  158 + }
155 159 if (file->f_op->open)
156 160 err = file->f_op->open(inode, file);
157 161 if (err) {