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fix(userspace/libsinsp/parsers): guard against invalid cmsg_len values #2768

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fix(userspace/libsinsp/parsers): guard against invalid cmsg_len values #2768

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24 changes: 15 additions & 9 deletions userspace/libsinsp/parsers.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3180,6 +3180,11 @@ struct ppm_cmsghdr {

#define PPM_CMSG_ALIGN(len) (((len) + sizeof(size_t) - 1) & (size_t) ~(sizeof(size_t) - 1))

// Given a length, return the additional padding necessary such that
// `len + __PPM_CMSG_PADDING(len) == PPM_CMSG_ALIGN(len)`.
#define __PPM_CMSG_PADDING(len) \
((sizeof(size_t) - ((len) & (sizeof(size_t) - 1))) & (sizeof(size_t) - 1))

#define PPM_CMSG_NXTHDR(msg_control, msg_controllen, cmsg) \
ppm_cmsg_nxthdr(msg_control, msg_controllen, cmsg)
static ppm_cmsghdr *ppm_cmsg_nxthdr(char const *msg_control,
Expand All @@ -3191,17 +3196,18 @@ static ppm_cmsghdr *ppm_cmsg_nxthdr(char const *msg_control,
return nullptr;
}

size_t const cmsg_aligned_len = PPM_CMSG_ALIGN(cmsg_len);
// Guard against infinite loop: ensure we advance by at least sizeof(ppm_cmsghdr)
if(cmsg_aligned_len < sizeof(ppm_cmsghdr)) {
return nullptr;
}
cmsg = reinterpret_cast<ppm_cmsghdr *>(reinterpret_cast<char *>(cmsg) + cmsg_aligned_len);
if(reinterpret_cast<char *>(cmsg + 1) > msg_control + msg_controllen ||
reinterpret_cast<char *>(cmsg) + cmsg_aligned_len > msg_control + msg_controllen) {
// There isn't enough space between cmsg and the end of the buffer to hold the current cmsg
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@terror96 terror96 Dec 29, 2025

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Suggested change
// There isn't enough space between cmsg and the end of the buffer to hold the current cmsg
// Check that there is enough space between cmsg and the end of the buffer to hold the current cmsg

// *and* the next one.
const size_t size_needed = sizeof(ppm_cmsghdr) + __PPM_CMSG_PADDING(cmsg_len);
const size_t remaining_room =
static_cast<size_t>(msg_control + msg_controllen - reinterpret_cast<char *>(cmsg));
if(remaining_room < size_needed || remaining_room - size_needed < cmsg_len) {
return nullptr;
}
return cmsg;

// Now, we trust cmsg_len and can use it to find the next header.
return reinterpret_cast<ppm_cmsghdr *>(reinterpret_cast<char *>(cmsg) +
PPM_CMSG_ALIGN(cmsg_len));
}

#define PPM_CMSG_DATA(cmsg) ((char *)((ppm_cmsghdr *)(cmsg) + 1))
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