Skip to content

fix(ip4defrag): allow final fragment to be less than 8 octets #1124

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
wants to merge 1 commit into
base: master
Choose a base branch
from
Open

fix(ip4defrag): allow final fragment to be less than 8 octets #1124

Show file tree
Hide file tree
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
2 changes: 1 addition & 1 deletion ip4defrag/defrag.go
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -176,7 +176,7 @@ func (d *IPv4Defragmenter) securityChecks(ip *layers.IPv4) error {
fragSize := ip.Length - uint16(ip.IHL)*4

// don't allow small fragments outside of specification
if fragSize < IPv4MinimumFragmentSize {
if ip.Flags&layers.IPv4MoreFragments != 0 && fragSize < IPv4MinimumFragmentSize {
return fmt.Errorf("defrag: fragment too small "+
"(handcrafted? %d < %d)", fragSize, IPv4MinimumFragmentSize)
}
Expand Down
23 changes: 21 additions & 2 deletions ip4defrag/defrag_test.go
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -165,12 +165,31 @@ func TestDefragTooSmall(t *testing.T) {
Flags: layers.IPv4MoreFragments,
}
if _, err := defrag.DefragIPv4(&ip1); err == nil {
t.Fatal("defrag: Minimum fragment size is supposed to be 8")
t.Fatal("defrag: Minimum fragment size is supposed to be 8, except for the final fragment")
}

ip1.Length++
if _, err := defrag.DefragIPv4(&ip1); err != nil {
t.Fatalf("defrag: Minimum fragment size is supposed to be 8, %s", err)
t.Fatalf("defrag: Minimum fragment size is supposed to be 8, except for the final fragment, %s", err)
}
}

func TestDefragSmallFinalFragment(t *testing.T) {
defrag := NewIPv4Defragmenter()

ip1 := layers.IPv4{
Version: 4,
IHL: 5,
TTL: 15,
SrcIP: net.IPv4(1, 1, 1, 1),
DstIP: net.IPv4(2, 2, 2, 2),
Id: 0xcc,
FragOffset: 0,
Length: 27, // Minimum fragment size -1 + header (20)
Flags: 0, // Indicate final fragment
}
if _, err := defrag.DefragIPv4(&ip1); err != nil {
t.Fatal("defrag: Fragment size smaller than 8 should be allowed for the final fragment")
}
}

Expand Down