[PATCH 5.4.y] of: module: add buffer overflow check in of_modalias()

[PATCH 5.4.y] of: module: add buffer overflow check in of_modalias()

[Uwe Kleine-König]

From: Sergey Shtylyov <s.shtylyov@omp.ru>

commit cf7385cb26ac4f0ee6c7385960525ad534323252 upstream.

In of_modalias(), if the buffer happens to be too small even for the 1st
snprintf() call, the len parameter will become negative and str parameter
(if not NULL initially) will point beyond the buffer's end. Add the buffer
overflow check after the 1st snprintf() call and fix such check after the
strlen() call (accounting for the terminating NUL char).

Fixes: bc575064d688 ("of/device: use of_property_for_each_string to parse compatible strings")
Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Link: https://lore.kernel.org/r/bbfc6be0-c687-62b6-d015-5141b93f313e@omp.ru
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Uwe Kleine-König <ukleinek@debian.org>
---
 drivers/of/device.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/of/device.c b/drivers/of/device.c
index 7fb870097a84..ee3467730dac 100644
--- a/drivers/of/device.c
+++ b/drivers/of/device.c
@@ -213,14 +213,15 @@ static ssize_t of_device_get_modalias(struct device *dev, char *str, ssize_t len
 	csize = snprintf(str, len, "of:N%pOFn%c%s", dev->of_node, 'T',
 			 of_node_get_device_type(dev->of_node));
 	tsize = csize;
+	if (csize >= len)
+		csize = len > 0 ? len - 1 : 0;
 	len -= csize;
-	if (str)
-		str += csize;
+	str += csize;
 
 	of_property_for_each_string(dev->of_node, "compatible", p, compat) {
 		csize = strlen(compat) + 1;
 		tsize += csize;
-		if (csize > len)
+		if (csize >= len)
 			continue;
 
 		csize = snprintf(str, len, "C%s", compat);

base-commit: 2c8115e4757809ffd537ed9108da115026d3581f
-- 
2.47.2

Re: [PATCH 5.4.y] of: module: add buffer overflow check in of_modalias()

[Sasha Levin]

[ Sasha's backport helper bot ]

Hi,

✅ All tests passed successfully. No issues detected.
No action required from the submitter.

The upstream commit SHA1 provided is correct: cf7385cb26ac4f0ee6c7385960525ad534323252

WARNING: Author mismatch between patch and upstream commit:
Backport author: <ukleinek@debian.org>
Commit author: Sergey Shtylyov<s.shtylyov@omp.ru>

Status in newer kernel trees:
6.14.y | Present (exact SHA1)
6.12.y | Present (exact SHA1)
6.6.y | Present (different SHA1: 0b0d5701a8bf)
6.1.y | Present (different SHA1: 5d59fd637a8a)
5.15.y | Present (different SHA1: 5bdbbfb49bec)
5.10.y | Present (different SHA1: 6df2777b9e01)

Note: The patch differs from the upstream commit:
---
1:  cf7385cb26ac4 ! 1:  c4addef3bafbd of: module: add buffer overflow check in of_modalias()
    @@ Metadata
      ## Commit message ##
         of: module: add buffer overflow check in of_modalias()
     
    +    commit cf7385cb26ac4f0ee6c7385960525ad534323252 upstream.
    +
         In of_modalias(), if the buffer happens to be too small even for the 1st
         snprintf() call, the len parameter will become negative and str parameter
         (if not NULL initially) will point beyond the buffer's end. Add the buffer
    @@ Commit message
         Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
         Link: https://lore.kernel.org/r/bbfc6be0-c687-62b6-d015-5141b93f313e@omp.ru
         Signed-off-by: Rob Herring <robh@kernel.org>
    +    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    +    Signed-off-by: Uwe Kleine-König <ukleinek@debian.org>
     
    - ## drivers/of/module.c ##
    -@@ drivers/of/module.c: ssize_t of_modalias(const struct device_node *np, char *str, ssize_t len)
    - 	csize = snprintf(str, len, "of:N%pOFn%c%s", np, 'T',
    - 			 of_node_get_device_type(np));
    + ## drivers/of/device.c ##
    +@@ drivers/of/device.c: static ssize_t of_device_get_modalias(struct device *dev, char *str, ssize_t len
    + 	csize = snprintf(str, len, "of:N%pOFn%c%s", dev->of_node, 'T',
    + 			 of_node_get_device_type(dev->of_node));
      	tsize = csize;
     +	if (csize >= len)
     +		csize = len > 0 ? len - 1 : 0;
    @@ drivers/of/module.c: ssize_t of_modalias(const struct device_node *np, char *str
     -		str += csize;
     +	str += csize;
      
    - 	of_property_for_each_string(np, "compatible", p, compat) {
    + 	of_property_for_each_string(dev->of_node, "compatible", p, compat) {
      		csize = strlen(compat) + 1;
      		tsize += csize;
     -		if (csize > len)
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-5.4.y        |  Success    |  Success   |