Skip to content

Fix unsigned underflow in buffer_check_limits() bounds check #273

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
kodareef5 wants to merge 1 commit into
base: main
Choose a base branch
from
+2 −1
Open

Fix unsigned underflow in buffer_check_limits() bounds check #273

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
3 changes: 2 additions & 1 deletion src/lib/buffer.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -57,7 +57,7 @@ buffer_check_limits(struct real_buffer *buf, size_t pos, size_t data_size)
{
size_t new_size;

if (unlikely(buf->max_size - pos < data_size))
if (unlikely(pos > buf->max_size || buf->max_size - pos < data_size))
Copy link
Copy Markdown
Contributor

@sirainen sirainen Mar 24, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This is a good fix, although commit message could say that this doesn't affect buffers created with buffer_create_dynamic(), which are most buffers, since then max_size == SIZE_MAX. Also commit title needs a lib: prefix.

Copy link
Copy Markdown
Author

@kodareef5 kodareef5 Mar 24, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Done. Added lib: prefix and noted the buffer_create_dynamic() / SIZE_MAX scope in the commit message.

i_panic("Buffer write out of range (%zu + %zu)", pos, data_size);

new_size = pos + data_size;
Expand Down Expand Up @@ -129,6 +129,7 @@ buffer_check_append_limits(struct real_buffer *buf, size_t data_size)
If it does, we don't even need to memset() the dirty buffer since
it's going to be filled with the newly appended data. */
#ifndef DEBUG_FAST
i_assert(buf->used <= buf->writable_size);
if (buf->writable_size - buf->used < data_size)
buffer_check_limits(buf, buf->used, data_size);
else
Expand Down