drivers/xen/grant-table.c: Be sure of unsigned value never comparing with 0

PATCH Applied Chen Gang 2 participants 9 messages Aug 26, 2014 – Aug 27, 2014 Xen hypervisor interface

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Chen Gang

author

2014-08-26 15:38 UTC #0 lore raw

PATCH 1/1 drivers/xen/grant-table.c: Be sure of unsigned value never comparing with 0

In grow_gnttab_list(), 'i' is 'unsigned int', and 'nr_glist_frames' may be 0 because 'nr_grant_frames' may be 0. So 'i' may never be less than 'nr_glist_frames' in failure processing, which cause infinite looping.

Signed-off-by Chen Gang <[email protected]>

---
 drivers/xen/grant-table.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

drivers/xen/grant-table.c +2 -2

index c254ae0..be07645 100644
@@ -592,8 +592,8 @@ static int grow_gnttab_list(unsigned int more_frames)
 	return 0;
 
 grow_nomem:
-	for ( ; i >= nr_glist_frames; i--)
-		free_page((unsigned long) gnttab_list[i]);
+	while (i > nr_glist_frames)
+		free_page((unsigned long) gnttab_list[--i]);
 	return -ENOMEM;
 }

Signature · 1 line

1.9.3

David Vrabel

2014-08-26 17:03 UTC #1 lore raw

Quoted 3 lines · Chen Gang

In grow_gnttab_list(), 'i' is 'unsigned int', and 'nr_glist_frames' may be 0 because 'nr_grant_frames' may be 0. So 'i' may never be less than 'nr_glist_frames' in failure processing, which cause infinite looping.

nr_grant_frames is at least 1. See gnttab_init().

drivers/xen/grant-table.c static int grow_gnttab_list(unsigned int more_frames) · line 596

Quoted 10 lines

drivers/xen/grant-table.c +2 -2

@@ -592,8 +592,8 @@ static int grow_gnttab_list(unsigned int more_frames)
 	return 0;
 
 grow_nomem:
-	for ( ; i >= nr_glist_frames; i--)
-		free_page((unsigned long) gnttab_list[i]);
+	while (i > nr_glist_frames)
+		free_page((unsigned long) gnttab_list[--i]);

while (i-- > nr_glist_frames)

...

Would have been better.

David

David Vrabel

2014-08-26 17:03 UTC #8 lore raw

In reply to Chen Gang

Quoted 3 lines · Chen Gang

In grow_gnttab_list(), 'i' is 'unsigned int', and 'nr_glist_frames' may be 0 because 'nr_grant_frames' may be 0. So 'i' may never be less than 'nr_glist_frames' in failure processing, which cause infinite looping.

nr_grant_frames is at least 1. See gnttab_init().

drivers/xen/grant-table.c static int grow_gnttab_list(unsigned int more_frames) · line 596

Quoted 10 lines

drivers/xen/grant-table.c +2 -2

@@ -592,8 +592,8 @@ static int grow_gnttab_list(unsigned int more_frames)
 	return 0;
 
 grow_nomem:
-	for ( ; i >= nr_glist_frames; i--)
-		free_page((unsigned long) gnttab_list[i]);
+	while (i > nr_glist_frames)
+		free_page((unsigned long) gnttab_list[--i]);

while (i-- > nr_glist_frames)

...

Would have been better.

David

Chen Gang

author

2014-08-26 19:43 UTC #2 lore raw

In reply to David Vrabel

Quoted 7 lines · David Vrabel

Quoted 3 lines · Chen Gang
In grow_gnttab_list(), 'i' is 'unsigned int', and 'nr_glist_frames' may be 0 because 'nr_grant_frames' may be 0. So 'i' may never be less than 'nr_glist_frames' in failure processing, which cause infinite looping.
nr_grant_frames is at least 1. See gnttab_init().

OK, thanks, that sounds reasonable to me, it is not a real wold bug, it is my fault. :-)

Quoted 12 lines

drivers/xen/grant-table.c static int grow_gnttab_list(unsigned int more_frames) · line 596
Quoted 10 lines
drivers/xen/grant-table.c +2 -2
@@ -592,8 +592,8 @@ static int grow_gnttab_list(unsigned int more_frames)
 	return 0;
 
 grow_nomem:
-	for ( ; i >= nr_glist_frames; i--)
-		free_page((unsigned long) gnttab_list[i]);
+	while (i > nr_glist_frames)
+		free_page((unsigned long) gnttab_list[--i]);
while (i-- > nr_glist_frames)

Quoted 4 lines

    ...
Would have been better.

OK, thanks, that sounds reasonable to me.

If necessary to send patch v2 (change comments and contents), please let me know, and I shall send.

Thanks.

Signature · 3 lines

Chen Gang

Open share and attitude like air water and life which God blessed

Chen Gang

author

2014-08-26 19:43 UTC #7 lore raw

In reply to David Vrabel

Quoted 7 lines · David Vrabel

Quoted 3 lines · Chen Gang
In grow_gnttab_list(), 'i' is 'unsigned int', and 'nr_glist_frames' may be 0 because 'nr_grant_frames' may be 0. So 'i' may never be less than 'nr_glist_frames' in failure processing, which cause infinite looping.
nr_grant_frames is at least 1. See gnttab_init().

OK, thanks, that sounds reasonable to me, it is not a real wold bug, it is my fault. :-)

Quoted 12 lines

drivers/xen/grant-table.c static int grow_gnttab_list(unsigned int more_frames) · line 596
Quoted 10 lines
drivers/xen/grant-table.c +2 -2
@@ -592,8 +592,8 @@ static int grow_gnttab_list(unsigned int more_frames)
 	return 0;
 
 grow_nomem:
-	for ( ; i >= nr_glist_frames; i--)
-		free_page((unsigned long) gnttab_list[i]);
+	while (i > nr_glist_frames)
+		free_page((unsigned long) gnttab_list[--i]);
while (i-- > nr_glist_frames)

Quoted 4 lines

    ...
Would have been better.

OK, thanks, that sounds reasonable to me.

If necessary to send patch v2 (change comments and contents), please let me know, and I shall send.

Thanks.

Signature · 3 lines

Chen Gang

Open share and attitude like air water and life which God blessed

David Vrabel

Applied

2014-08-27 10:06 UTC #3 lore raw

In reply to Chen Gang

Quoted 26 lines · Chen Gang

Quoted 7 lines · David Vrabel
Quoted 3 lines · Chen Gang
In grow_gnttab_list(), 'i' is 'unsigned int', and 'nr_glist_frames' may be 0 because 'nr_grant_frames' may be 0. So 'i' may never be less than 'nr_glist_frames' in failure processing, which cause infinite looping.
nr_grant_frames is at least 1. See gnttab_init().
OK, thanks, that sounds reasonable to me, it is not a real wold bug, it is my fault. :-)
Quoted 14 lines
drivers/xen/grant-table.c static int grow_gnttab_list(unsigned int more_frames) · line 596
Quoted 10 lines
drivers/xen/grant-table.c +2 -2
@@ -592,8 +592,8 @@ static int grow_gnttab_list(unsigned int more_frames)
 	return 0;
 
 grow_nomem:
-	for ( ; i >= nr_glist_frames; i--)
-		free_page((unsigned long) gnttab_list[i]);
+	while (i > nr_glist_frames)
+		free_page((unsigned long) gnttab_list[--i]);
while (i-- > nr_glist_frames)
    ...

Quoted 7 lines

Quoted 2 lines
Would have been better.
OK, thanks, that sounds reasonable to me.
If necessary to send patch v2 (change comments and contents), please let me know, and I shall send.

Applied to devel/for-linus-3.18 with this description:

xen/grant-table: refactor error cleanup in grow_gnttab_list()

The cleanup loop in grow_gnttab_list() is safe from the underflow of the unsigned 'i' since nr_glist_frames is >= 1, but refactor it anyway.

Thanks.

David

David Vrabel

Applied

2014-08-27 10:06 UTC #6 lore raw

In reply to Chen Gang

Quoted 26 lines · Chen Gang

Quoted 7 lines · David Vrabel
Quoted 3 lines · Chen Gang
In grow_gnttab_list(), 'i' is 'unsigned int', and 'nr_glist_frames' may be 0 because 'nr_grant_frames' may be 0. So 'i' may never be less than 'nr_glist_frames' in failure processing, which cause infinite looping.
nr_grant_frames is at least 1. See gnttab_init().
OK, thanks, that sounds reasonable to me, it is not a real wold bug, it is my fault. :-)
Quoted 14 lines
drivers/xen/grant-table.c static int grow_gnttab_list(unsigned int more_frames) · line 596
Quoted 10 lines
drivers/xen/grant-table.c +2 -2
@@ -592,8 +592,8 @@ static int grow_gnttab_list(unsigned int more_frames)
 	return 0;
 
 grow_nomem:
-	for ( ; i >= nr_glist_frames; i--)
-		free_page((unsigned long) gnttab_list[i]);
+	while (i > nr_glist_frames)
+		free_page((unsigned long) gnttab_list[--i]);
while (i-- > nr_glist_frames)
    ...

Quoted 7 lines

Quoted 2 lines
Would have been better.
OK, thanks, that sounds reasonable to me.
If necessary to send patch v2 (change comments and contents), please let me know, and I shall send.

Applied to devel/for-linus-3.18 with this description:

xen/grant-table: refactor error cleanup in grow_gnttab_list()

The cleanup loop in grow_gnttab_list() is safe from the underflow of the unsigned 'i' since nr_glist_frames is >= 1, but refactor it anyway.

Thanks.

David

Chen Gang

author

2014-08-27 10:22 UTC #4 lore raw

In reply to David Vrabel

Quoted 9 lines · David Vrabel

Applied to devel/for-linus-3.18 with this description:
xen/grant-table: refactor error cleanup in grow_gnttab_list()
The cleanup loop in grow_gnttab_list() is safe from the underflow of the unsigned 'i' since nr_glist_frames is >= 1, but refactor it anyway.

OK, thank you very much for your encouragement! And next, I shall try to provide another patches for Xen (hope I can finish within this month). And I should be more careful about the patches which I shall send.

Also I want to consult: "Is there a common test for Xen"? If there is, please let me know, and I should try to perform the common test before send any patches.

Welcome any additional ideas, suggestions, and completions.

Thanks.

Signature · 3 lines

Chen Gang

Open, share, and attitude like air, water, and life which God blessed

Chen Gang

author

2014-08-27 10:22 UTC #5 lore raw

In reply to David Vrabel

Quoted 9 lines · David Vrabel

Applied to devel/for-linus-3.18 with this description:
xen/grant-table: refactor error cleanup in grow_gnttab_list()
The cleanup loop in grow_gnttab_list() is safe from the underflow of the unsigned 'i' since nr_glist_frames is >= 1, but refactor it anyway.

Also I want to consult: "Is there a common test for Xen"? If there is, please let me know, and I should try to perform the common test before send any patches.

Welcome any additional ideas, suggestions, and completions.

Thanks.

Signature · 3 lines

Chen Gang

Open, share, and attitude like air, water, and life which God blessed